If I pre approve, can the guest still change their dates?
The origional request was to check in on Friday- Friday, but due to the availability of my apt, they can only check in Sat- Sat. I made this clear to them via email, but pre- approved their request. Can they go back and change the dates to Sat- Sat before booking?
You can remove your current pre-approval since those dates won't work.
Since it was just an inquiry they can create a reservation request for the Saturday to Saturday dates. Or submit another inquiry for the S-S dates which you can then pre-approve.
Yes, they will be able to book you place with the changed dates. The pre-approval is not a confirmed reservation, it is only your agreement they can book with you based on your availability. Sometimes even after getting the pre-approval guests will pick another location they find more to their liking instead.