Removing the pump body is the Toyota recommended method to remove and replace the seal. It is possible to jam a screwdriver in there and scratch everything all to hell, just for the sake of applying the perceived minimal possible effort. It will be far easier to R&R the seal with the body out, and only takes a minute of your time to pull the body out and do it correctly. The seal has a steel body that can damage easily if you try to whack it in there with a socket or hammer. With the body out you can gently tap it in with a flat object & hammer, or with some sort of press, like the arbor press in the picture.
Your tranny is already out, finish it up correctly. I'd even press it in for you if you lived nearby.