It's difficult to give advice without actually seeing the changes in context. The following assumes we're talking about a question of your own, and not someone else's...
A good rule of thumb is to look at the current answers to the question. If your edits would leave the current answers making no sense, then you shouldn't make them.
If your edits mean that the current answers would still answer the original question, and that original question is still part of the new question body, I don't see any harm at all in expanding it.
But while doing that, just make sure that you're not broadening the question beyond the scope allowed by the FAQ. It might well be that you need a new question that refers back to the bountied one, it really depends.