or do you have to go ahead with choosing and then playing the card you select?
A: This would ultimately be your call: how lenient do you want to be about letting people take back plays? You should form a house rule about this that everyone is clear on before they start.
But for perspective, this is how we usually rule it:
We have always played that, since anyone may look through the discard pile at any time (as it says on the Rewind card), one should check before playing a Rewind, and not play it if there isn’t something you want there. So we’ve always been lenient if someone played it, checked and realized there wasn’t what they needed, since it’s no skin off anyone’s back that they just looked through the pile after playing the card instead of before. They can retract their play, since looking through the pile is an action that made no difference to the game (except they revealed they have a Rewind, which is only bad for them – the cost of any play retraction “oopsie”).
Looking through the draw pile, however is hidden information, and we’ve always ruled that once you look through that, which you can ONLY do if you play a Quick Trip, then you DO have to choose _something_ and immediately play it. You can’t take back having seen what cards remain in the draw pile – so you can’t take back that play.