how would it affect a player to roleplay as the active/passive opposite of their class, ex. a witch roleplaying as an heir or a bard roleplaying as a prince?

Depends- For Classes like the Witch or the Seer, and even a bit the Rogue and Page, they have more ease switching between Passive and Active. Princes and Maids have a harder time- The more ‘versatile’ a Class is, the easier it is to flip between a passive and active role, so a Witch acting like a Heir would be much more healthy than a Maid trying to be a Sylph. Still though, holding back your true desires and repressing more selfish or selfless impulses may still be damaging in the long run.