When I had my 89 Vic, my dad broke the driver's side taillight.

When the part came in, I noticed I only received the lens, and not the whole light piece, but I couldn't figure out how to get the dang thing apart. The lens seemed to be glued into the fixture itself. Since my dad broke it, I made him fix it.

He used a screwdriver and
gently pried between the lens and the fixture. (The fixture is plastic, too!) IIRC it came out without much trouble, though I do seem to remember some broken lens pieces. I can't say for certainty whether it came out in one piece or not.
In order to affix the new lens in the fixture, it came with a roll of black sticky stuff that I just laid down in the fixture where the original lens was glued in. Pressed the new lens into place and bingo, looked just fine. Had the car for 4 years like that after with no issues at all. I'm not sure what that black sealer is or is called, I think I still have a little bit of it left somewhere but it's probably hard as a rock now.
Don't know if that helps, I guess the lenses are really a "one-time-use" thing.