How game-breaking would a house-rule letting spellcasters prepare new spells at any time be?

Question

Spellcasters that prepare spells have nearly identical rulings when and how they can do so (emphasis mine):

You can change your list of prepared spells when you finish a long rest. Preparing a new list of class spells requires time spent studying/meditating: at least 1 minute per spell level for each spell on your list.

To give my players more flexibility, I want to drop the bold part and allow them to prepare new spells any time they want. They would still need the time to study/meditate, i.e. it would not be an option in the middle of a fight.

Also, RAW it seems that you would always have to spent time for each spell on the list. To speed this up, I would only require study/meditation time for spells that they did not have prepared before, so e.g. replacing a single spell just takes a few minutes.

In general, this would allow to prepare more combat spells and being able to utilize more utility spells at the same time.

Of course, this would step on the toes of wizard with their superior ritual casting, because clerics and druids now only need a few more minutes to prepare the ritual spells just when needed. However, this is not a problem in my group, because we do not have a wizard.

Apart from that, how game-breaking would this rule be? In particular, would it make the preparing spellcaster classes overpowered rather than giving them just more utility?

Answer 1

It depends on what you mean by game breaking, exactly.

But it will be seriously imbalanced in that it makes casters that prepare spells much more attractive than casters with known spells.

It turns out that you're not as concerned about Wizards, which were my base example below. This houserule would be especially powerful for them, but my arguments work just as well for other class using prepared versus "known" spells. Additionally, your players would gain a lot by multi-classing into Wizard with this rule in place.

Advantage: prepared casters

The big issue is that spell flexibility doesn't make the spells themselves any more powerful, but it does make casters that prepare spells effectively more powerful. It will also make a lot of challenges much less difficult for players. And, depending on your players, it might drain some of the interest away from casters that use preparation-- when I play a wizard, choosing which spells to prepare is a major strategic choice and a big element of gameplay.

For example, a Wizard ordinarily has to make a lot of decisions about what spells they want available during a dungeon crawl, because they're stuck with what they pick. Do they take something useful in adventuring, like detect magic, or something useful in combat, like magic missile? It can be a tough call, and the flexibility a magic user has is balanced by the risk of bringing spells that aren't useful at all.

With this houserule those choices and decisions disappear. If a Wizard sees a situation where they might want to cast detect magic, they just need one in-game minute and then they can. After they've tried it, they can just drop it for a combat spell instead. A canny spellcaster might be loaded for bear with combat spells most of the time (plus maybe one or two that can help in an acute crisis as a reaction), and will become perfectly situated to address any dungeon hazard they encounter at any time.

It will be most valuable for Wizards, as they have the largest spell list and the most spell slots. Their spell slots would become incredibly versatile at a (usually) negligible cost, at most nine minutes' wait. The value of this houserule to preparation-requiring casters is a function of spell list size, spell effect variety, and number of spell slots available.

Spellcasters that don't need preparation will become less important. Truly unique effects will be as useful as ever, but outside of those they'll be increasingly relegated to "common" things since the opportunity cost of using a preparer to do them will be higher. It's already often an unusual choice to use a wizard to cast a healing spell, for example, since they can do so many other things with a spell slot that other classes can't. The increased flexibility of changing prepared spells on the fly exacerbates that, leaving non-preparers to fill in the gaps.

Some incentives will change as a result:

• Casters will be well-advised to accumulate as many spells as possible, because they'll all be similarly available at need.
• Some spells, like chromatic orb, will lose some of their cachet, since specific damage types will be more accessible with very little lead time.
• Some class features may become more attractive as well, particularly those which restore spell slots or expand the spell list available to a character.
• Multi-classing to expand spell lists will become extremely attractive, though the synergies that become possible might be interesting enough to add a new dimension to gameplay (just one that happens to be focused more around magic users).
• Scouting and sneaking in dungeons becomes more attractive, as advance knowledge of opponents makes hard-counter preparation much easier. The party will essentially never encounter an enemy with an immunity or resistance that hampers one of their spells, or a weakness they can't exploit, and enemies will have a much more difficult time exploiting weaknesses among the party.
• Casters that don't need preparation will lose some of their value, since they'll gain no benefit while other classes become even more flexible and responsive, and if some of their spells are available (or can be effectively duplicated) by a caster needing preparation those classes will be less useful.
• Finally, I think that you might see a lot more incentive for short rests. Since the casters will need some downtime anyways, it becomes more and more attractive to stretch that downtime a bit farther so the caster gets a perfectly tailored spell list for their situation, and all the other players get the benefits of a short rest as well. Though that's a secondary effect which is under your control as DM, a party that takes short rests more frequently will find challenges easier than if they'd not rested.

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Final Thoughts:

I think that this could be a really interesting houserule, but it might work best in a campaign specifically designed to accommodate it. Something high-magic, where the flexibility is expected and built into the challenges. Perhaps with all players taking classes that will benefit right from the start. But in a normal campaign, with players making character choices before knowing about this rule, I think that this would be destabilizing and highly game-able.

Answer 2

I want to add to other answers on the main aspect that gets broken by this rule, IMO

Based on experience, the tradeoff between "spontaneous" casters (bards, rangers, sorcerers and warlocks) and "prepared" casters (clerics, druids, paladins, wizards) is that the spontaneous casters have access to a much more restricted spells list, unless the DM is running a very low magic games where even spellsbooks and scrolls and very rare.

Focusing on those classes most affected by this rule for simplicity's sake, aka the "full spellcasters" (bards, clerics, druids, sorcerers, wizards), every one of them gets to cast the same numbers of spells and the main differences (besides subclass, fluff and stuff, etc.) is the spells they chose on level ups.

Clerics and druids get access to their full list of spells and can chose everyday. A wizard can get there eventually by copying every written spells and/or paying to be taught more spells as they progress while all spontaneous casters won't ever get this possibility ... the spells they chose every time they level are what they get, nothing more.

Thus, this rule really cripples bards and sorcerers the most, and to a lesser extent all other sub/classes that are limited in the number of spells they learn on each level.

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Unless accompanied by another rule to allow arcane spellcasters to learn all the spells they want, this is too game breaking

Making it into a feat or magical item as suggested by Valley Lad is less game breaking, but it still breaks the game too much to my liking. Removing the "Spells known" vs "Preparing spells" difference between the two types of full spell casters only serves to make like half of them basically crippled. It is also a feat and magic item that all of your clerics, druids and wizards players would take, it'd be such a no brainer at least for me.

Unless you add another house rule allowing spontaneous spellcasters to learn spells for a price, just like the wizard, then I would bet that implementing this rule before PC creation makes it so no one ever plays a bard or sorcerer in your game, or they ask for a new character soon after if it is done mid-game.

Answer 3

Consider making it a feat or a magic item, so that it is not so unbalanced

In keeping with Upper_Case's answer, I believe you are left with the conclusion that it would make the game unbalanced. In that case, I believe you could offer the benefit in the form of a feat, so that the player has to give up an ASI to get it, or you could put it in the form of a magic item requiring attunement, so that the player has to give up an attunement slot (after earning the magic item, as well).

I'll give a couple examples by way of illustration (bearing in mind these are untested).

As a feat, it might look like this:

Spellmind

Prerequisite: The ability to prepare spells.

You've spent much time and effort learning how to change your prepared spells with a short duration of meditation. You gain the following benefits:

• You can change your list of prepared spells when you finish a short rest. You can do this a number of times each day equal to your spellcasting ability modifier for that spell list (minimum 1).

• Once per day you can replace a single spell on your spell list in a number of minutes equal to that spell level, with no further rest required. If the spell is of the highest level you can cast, then doing so causes you to increase one level of exhaustion.

As a magic item, it might look like this:

Circlet of Spell Preparation

rare (requires attunement)

While attuned to this circlet and wearing it, you can change your list of prepared spells when you finish a short rest. You can do this a number of times each day equal to your spellcasting ability modifier for that spell list (minimum 1).

Additionally, once per day you can replace a single spell on your spell list in a number of minutes equal to that spell level, with no further rest required. If the spell is of the highest level you can cast, doing so causes you to increase one level of exhaustion. Note that in both of these I wrote it as still requiring a short rest, because even the reduction from a long to a short rest is a major boost of flexibility and power, seeing that short rests are much easier to come by without encountering rotating guards or wandering monsters, etc.

The reason these would move toward balance, is that the house rule you are making is arguably on par with a feat or a magic item. For example, the ring of spell storing also enables a mage to effectively increase the number of prepared spells available without requiring rest to change them; and it is a rare item that requires attunement. Meanwhile there are various feats that give benefits to casters, like spell sniper, which are arguably on par with the increase in power that your house rule represents.

But if the way I wrote these up seems heavy-handed in any regard, you could take away the short rest requirement, or make the feat a half-feat, or take out the exhaustion side-effect, but I would do something like one of the above entries, so that the spell-preparers aren't getting a huge freebie relative to other classes.

Again, these are just untested examples for illustrative purposes. A reasonable way to move forward and ensure balance, would be to take something like the above (tuned to your own liking) and present on this stack as question of the form "Is this homebrew feat (or magic-item) balanced?"