> When using C++ I wanted programs to have a function that was called before main() and set up things that got sealed afterwards, like parsing command-line-arguments, the environment variables, loading runtime libraries, and maybe look at the local directory, but I'm not sure if it'll be a useful and meaningful distinction unless you restructure way too many things

If you're only reading environment variables you have no problem, though. It's only if you try to change them that it causes issues.

For setting, "only set environment variables in the Bash script that starts your program" might be a good rule.