You must call (or send an email to) MS to do the following:
- modify a reservation (add/drop nights at the start/end of your reservation)
- modify a wait list
- use transferred points (unless the points you transferred in are an exact match for the resort and UY of one of your contracts)
- purchase one-time-use points
- merge reservations, for example to merge additional nights you booked online that are just before or after an existing reservation with your existing reservation
- link two reservations booked under separate memberships that are actually one continuous stay (same resort, room size, booking category) so that the room assigner puts you in the same room for the entire stay
- add requests to a reservation (ex: "top floor")
The things you mentioned (set up a wait list, bank or borrow) can be done online. You can also cancel a reservation online.