If you change your Wizard subclass from Chronurgy Magic to something else, do you retain the subclass-specific dunamancy spells you've learned?

Question

For reference, Tasha's Cauldron of Everything (p. 8) adds official (optional) mechanics for changing your subclass. It states, in part:

[...] With your DM’s approval, you can change your subclass when you would normally gain a new subclass feature. If you decide to make this change, choose another subclass that belongs to your class and replace all your old subclass features with the features of the new subclass that are for your new level and lower.

Explorer's Guide to Wildemount adds 2 new subclasses for wizards (Chronurgy Magic and Graviturgy Magic), as well as several new dunamancy spells. The "Dunamancy for Non-Dunamancers" sidebar states (p. 186):

Dunamancy spells are readily available to the wizard subclasses in this chapter and should not be simply added to the full spell list of other spell casting classes. [...]

When you change your subclass, your previous subclass features are replaced with the new subclass features. The dunamancy spells are not technically a subclass feature, but to learn them you do have to be a specific wizard subclass.

Do you lose access to dunamancy spells that you have learned and written in your spellbook if you choose a new subclass that does not have access to dunamancy?

Answer 1

You know what you know.

The intent of the sidebar, taken as a whole, is "dunamancy is rare and protected, and it requires DM permission to learn if you aren't a trained dunamancer", but since dunamancer subclasses can use any of these spells as much as they like, this doesn't seem to be for balance reasons. It's just the flavor of the setting.

From a rules perspective, your spellbook is what it is. The sidebar says any wizard can add dunamancy to their spellbook if they're specifically allowed to, and you had permission by dint of your subclass, so you're fine there.

From a flavor standpoint, when you learned those spells, you were in fact a dunamancer, and then later you changed your subclass for whatever reason. You probably won't be able to add new dunamancy spells to your book without the DM providing them to you, but the existing knowledge doesn't evaporate.

But ask your DM.

Changing your subclass is always "with DM approval", and always a conversation to determine why and how it's going to happen. It doesn't actually matter what the sidebar and the "changing subclasses" rules say; it's between the two of you at the table to come up with a story and determine the answer to questions like how it impacts your known dunamancy spells. There is no set of rules that can override your personal discussion with your DM.

If you talk it over with the DM and decide that you're just changing your focus for character reasons, but you'll be allowed to keep your dunamancy spells, then you have the necessary DM permission to keep them. It doesn't matter whether or not that's strictly according-to-sidebar; the DM says that's how it'll work.

If you and the DM mutually decide that you've somehow lost your magical connection to dunamis, then maybe all dunamancy is now out of your reach, and the spells are still there in your book, but useless to you. The DM should probably take into account that you've lost a bunch of spells off your list and make an effort to let you replace them with non-dunamancy spells. Maybe later you'll regain your connection and re-acquire all those lost spells, again with the DM's permission.

If you and your DM decide that your character is intentionally turning their back on dunamancy, believing it to be dangerous or unethical, maybe you rip those pages out of your spellbook and burn them, swearing never again to use that power. In that case, then you have your answer (and the DM should again give you the opportunity to replace them).

Ultimately, it's not about what the book says, because before it tells us what the rules are, the book first says that all the rules are "if the DM wants to allow it".

Answer 2

You do not have to be a Chronurgist or Graviturgist to learn Dunamancy spells. Having the spell written down is sufficient.

The assertion you make in the question is incorrect, the rest of the paragraph that you quoted explains this quite plainly:

However, the Dungeon Master can consider allowing other spellcasting classes opportunities throughout the campaign to learn a handful of dunamancy-themed spells as rewards. Perhaps the characters uncover a cache of magical contraband, among which is a couple of spell scrolls, or a traveling acolyte takes some downtime with a friendly cleric character and opens their mind to some of the stranger secrets of the universe, unlocking a spell or two. There are many unique ways to bring these spells into your game without requiring any specific dunamis-wielding subclasses to be present in the adventuring party.

Only Chronurgy and Graviturgy wizards can learn these spells when leveling up, but wizards of any class can learn Dunamancy spells using the "found spell" method. Once the spells are written in your spellbook you have access to them. One of the suggested methods for a DM to provide these spells is through found spell scrolls:

Perhaps the characters uncover a cache of magical contraband, among which is a couple of spell scrolls

Thus, a wizard that finds a Dunamancy spell is free to write it down in their spellbook as usual. But a wizard changing from Chronurgy or Graviturgy to another wizard subclass already has the spells written down. So they retain access.

That said, use and continued use of these spells is always subject to the DM's permission.