so, I was borrowing a mamiya 7 from school for a landscape class. I shot two rolls and put two shots on another roll. I ended up shooting the rest of the roll with the lens cap on because I had to give the camera back.
My question is whether it is feasible to assume I can simply reverse the roll AGAIN onto another spool so that it's going the right way. or can I just shoot it backwards? or do I develop the 2 shots that are on the roll and throw the rest out?
You can't shoot it backwards.
The film is only taped to the backing paper at the other end, and it and the paper will separate, producing a big mess inside the camera, when you try to run the film backwards through the thing.
Some people do respool, but is a fiddly business i would't want to try.
I would just process the film.
Film is cheaper than the two shots you put on it already. So why risk those two, only to save on a bit of film?
Respooling is not so difficult - I do it all the time for my 620, but to save a roll of film - wouldn't bother. Better to process the film with the 2 images on it. The time you spend trying to respool correctly so that you can shoot the rest of the roll would be better spent elsewhere.
As Q.G. said, "Film is cheaper than the two shots you put on it already."