One the reservation is in your name, even if it is through someone else's points, can you access it?
For example, would you be able to call and add things or make an adjustment on the reseravtion or would I have to go through the DVC member who booked it originally?
For most things, like dining plan and magical express, the DVC member that owns the points will have to add it for you. For dining plan, since payment is involved, you need to work out details with the DVC member. But you can make dining reservations yourself.
Other than making dining reservations, most other things, whether simple things like adding a note for special room request or more complicated like arranging grand gatherings, need to go through the DVC member.