For Star Tours, they may not be able to do it at the time you request it and may give you a time to come back. Whether or not they can do it right away depends on the number of cars they have running and the amount of staff currently working on the ride.
Access is easy. The ride car is a medium size theater. The front row has about 5-6 feet between the edge of the seats and the front of the 'stage' area. The front door is wide enough to pull a wheelchair or
ECV into the theater. The seats are individual seats for each person. You can pull right up to the seat (the wheelchair can even be touching the seat). Then you transfer to the seat and the CM pulls the wheelchair back out of the theater. After the show, they will move the wheelchair back for you.
That is how it works in the 'full-motion' version. I don't know if they would let someone stay in their wheelchair for the non-motion, movie only version.
We have not been on Mission Space since they added a less intense version, but my understanding is that they removed the spinning, but not the motion. People who have been on it have described it as about as intense as Star Tours. I don't know if they are able to do a non-motion version.
The only other simulator type ride they have was Body Wars, which was very much like Star Tours and they could do a non-motion version of that. The Wonders of Life pavilion has not been open for a long time, so I'm not sure that Body Wars even exists anymore.
The other more 'wild' rides are not simulators, so there isn't a way to offer a lower motion version.