Re
Well, you could play Neverwinter Nights...
As a Matter of fact, Sorcerers are quite a bit stronger than Wizards in Neverwinter Nights in large part because the can swap their spell every level.
With the rest period it takes to get spells back. I didn't notice much difference between the sorcerer and the wizard except the sorcerer could cast a few more spells he or she knew and the wizard could change out spells instantly depending on what he or she needed for the battle.
I actually think the wizard was a little more powerful than the sorcerer in NWN. If my sorcerer took on an enemy that was very magic resistant that I couldn't hurt he could not prepare any differently except with scrolls. If my wizard took on enemy he couldn't hurt, he just went outside the room, changed spells, rested 30 seconds and was ready to go. Sorcerers are not really stronger than wizards in NWN in my opinion.
Just more offensively powerful, like in actual D and D.
Not game breaking, just unfair to others.
I dont' think allowing a sorcerer or bard to switch spells through some arduous process that costs time and xp and requires a relatively high spellcraft roll is gamebreaking.
The disadvantage of playing a sorcerer would hardly be offset by being able to change out a few spells over the course of the life of the sorcerer. The only way this would be so is if the process of changing was so easy that a sorcerer could change spells as easily as wizard.
My campaign right now allows sorcerers the same number of bonus feats as a wizard and also gives the bonus feat eschew materials at first level. I also allow sorcerers bonus spells known for a high intelligence. I also allow bards with high intelligence to have bonus spells known.
The reason I did this is because no one wanted to play a sorcerer or a bard prior to the addition of these rules. The classes were too limiting and lacking for most players. Spell variety and little bonus abilities are what make the game fun for many players. Sorcerers seriously lack level based class abilities.
This has had no impact on my game. Wizards are still played more often than sorcerers. Why? With the addition of the Tome and Blood and Magic of Faerun, very few people want to give up the spell variety of a wizard to be able to cast 2 more spells per level. The benefit just doesn't outweigh the cost. This is probably the main reason I spiced up the sorcerer.
Currently, only two people have played bards. One is playing one because they are on the bladesinger path, and thought the bard fit well as a background class for a bladesinger. The other bard wanted to be a harper, so is playing a bard/ranger to be the archetypal harper. My house rules have in no way upset the fun or balance of the sorcerer or bard class.
Unless a rule imbalances the class or makes it much more powerful than their base class counterparts, I dont' see a problem with it. As far as being unfair to the other players because they can't change out their skills and feats, I don't see it.
I haven't seen one feat that isn't as good or necessary at the level you pick it up when compared to using the same feat at high level. If you can tell me one level dependent feat, that would be great.
As far as skills go, if there were some kind of skill degradation system as their is in a few other games, then I might see a person changing skills. I usually require my players to use at least half their skill points to boost skills they have used during an adventure.
Also, I know few folks who would have any motivation to adjust their skills at a later time. If some player really wanted to do this, then I would probably allow them to do so. I like players to enjoy the game. My main requirement is always to have some kind of roleplaying reason why a change is occurring.
I can think of plenty of reasons a sorcerer or bard might change spells out. Both classes are adventurous. A sorcerer might find some new spell he likes better, and decide that he wishes to practice that spell exclusively over some other spell he knows. A bard might feel the same way about a new spell, which is basically a new song to a bard. Why shouldn't either class be able to change a spell if they find one the like better? Is there a roleplaying reason why they should not or simply a game balance reason? I will always go with the roleplaying reason for something before I stick to a game balance or rule reason.
I simply can't think of one roleplaying reason why a sorcerer or bard would not be able to swap out spells. I see no reason to disallow it. I just think it should be a very difficult and time consumiing process.