Actually, the points are worthless to you if you are not a member. You are really renting a reservation made in your name from the member. You have no control over the reservation. It still belongs to the member and they could change it at any time. However, in the name of good will and ethics, I doubt if they would cancel it or rent it out to someone else if they have already taken money from you for the reservation.
Two studios could be more expensive than a one bedroom villa. The member could charge you a "change fee" to make the changes if they wanted to as well as a charge for additional cost for the reservation. If you have a contract signed with them, read it over to see what they say about changes.
The two studios may not even be available at this point, depending on the dates of the current reservation.