I have a question about opam. I would like to play with certain compiler
versions, but I don't want the switch to happen globally, because I still
need to compile regular code. Is it possible to switch to another compiler
locally (within a particular shell session) via environment variables,
while using my regular compiler in another shell session?

If this is the way things work already, I apologize in advance -- it
appeared to me that running opam switch modifies some global state that
directly affects other pre-existing shell sessions.

-Yotam