I have a party consisting of two PCs; a lv5 fighter (3 fighter, 1 rogue, 1 barbarian) , and a lv5 ranger (4 ranger, 1 cleric).
Focusing on the ranger for the purposes of this question. She doubles as our caster, and it's been working super well for us. However, we're feeling really hemmed in by the way prepared spells are managed in 5e. As a GM I don't like a) hounding her to pick spells after each long rest and b) limiting what they can do just because she didn't magically see into the future to realize Comprehend Languages would have been useful today.
I want to change how she prepares spells to allow her the roleplaying freedom to pick some spells at the time of casting, rather than needing to set them ahead of time. On the flip side I can see a lot of room for abuse so I'm considering offering one of the following two systems but would like someone to double check my logic (I'm a first-time GM and fairly unaware of what the later levels will bring.)
At this point her prepared spells work out like so;
She has access to eight spells total. Five are predetermined; three because she's a ranger and knows those spells, and two which are always prepared for her because of her cleric domain. This leaves three spells she must prepare at the beginning of each day.
I see two logical ways to resolve this.
Of the three remaining prepared spells, one can be swapped at will at the cost of an action. The other two must be prepared ahead of time like normal.
IE, she can take a turn during combat to switch one spell for another spell of her choice (or prepare one if the slot was previously empty).
Needing to take an action to prepare the spell should be enough of a limiter to prevent abuse, and it gives her plenty of flexibility during combat. However, outside of combat it would logically follow that she can switch spells, at will, every 6 seconds. That seems pretty game breaking.
The remaining prepared spells are empty until used. She can declare the use of a spell at any time for no penalty, but once the spell is declared she can't switch it again until the next long rest.
IE, over the course of a day she can select any three spells she likes to use but there's no option to change them once selected.
This feels more balanced between in-and-out of combat scenarios, but I can see it potentially getting out of control in later levels. I was thinking of restricting this down to just 1-2 "empty" prepared spells (the rest would be pre-prepared as usual) as a limitation if three is too broad.
I want to give my player more flexibility in her prepared spells. Is one of these two methods more acceptably balanced than the other? Will it become unbalanced as she levels up?