I'm puzzled

• we have shown you how to -> set the ENV of a sub process
• we have shown you how to -> get the ENV of a sub process

If that's not enough, maybe just better show us an SSCCE of what you want, instead of leaving us the burden of interpretation?

update

> All the commands run in the parent process.

Does that mean Perl is just the sub-process and you want to change the ENV of the non-Perl parent?

I'm afraid that's not possible, w/o adjusting the parent.

Already on the OS level this is forbidden for security reasons. The parent-process has full control and must actively change its own ENV. It is protected from changes in a sub-process.

Simplest solution: -> eval-ing a string returned by the Perl sub-process to set ENV

But now you are also confronted with security implications, because you have to make sure this communication isn't eavesdropped.

update

and if all of this doesn't help, please have a look there -> "I know what I mean. Why don't you?"