In the past, I have changed the AWD for a reservation (not changed in my profile) several times and the reservation reflects the other (non-profile) AWD.
In fairness, most, if not all, of these reservations have been at local (i.e. non-airport) locations. So the impact on Preferred/AF services is a little unclear since Preferred services are seldom available at non-airport locations.
That said, this coming weekend I have a reservation (made online) in which I have entered an AWD different than my profile at an airport location. This reservation reflects the other AWD. I'll report back if Preferred services were negatively impacted.
IME preferred services aren't impacted - the rate & AWD are. Eg. when my personal AWD was in the profile and my corp travel agent made a reservation, the reservation confirmation showed the correct corp rate and credit card #. When I pulled the record up a couple of weeks later, the record was updated to reflect my personal AWD rate (lower, actually, but not permitted for corporate travel). As per Avis, the only way to fix it was to cancel, change the AWD in the profile and rebook. Avis told me that the approved method of having multiple AWD numbers is to maintain multiple wizard numbers (which would not be cumulative wrt rental credits).