I just replaced my shift bellow this past weekend. I did have to pull the drive but I was able to complete the shift bellow swap without removing the bellhousing. I had to buy the specially socket and remove the shift cable housing from the bellhousing after I slid the cable core out. It looked like the cable housing would kink and damage it if I tried to slide it out of the transom without undoing it at the bellhousing end. Once I got the cable housing lose, slid out and the old bellow removed I slid the cable housing back through the bellhousing, inserted the shift cable housing through the new shift bellow about 3" (hardest part of the whole job), put the SS clamp around the bellow, put some bellows adhesive on the bellow and attached it on the transom, slid the SS clamp up and tightened it up with a socked and wobble attachment, slid the rest of the shift cable housing into the boat and tightened it back into the bellhousing with my new special socket, slid the shift cable core back in and reattached it to the shift plate, done. While I had the drive of to fix the shift bellow I went ahead and replaced my impeller, greased the gimbal, u-joints and checked my alignment. Wasn't difficult but did take me most of a day to complete.
