No, the parent process will not have its ENV variable changed, since you're forking off a subprocess when you run a Perl script, and when control comes back to the parent, the original environment is restored.

If I may suggest an alternative way ... use a statement like:

use lib [library path];
[download]

where [library path] is the path of the modules you want to include.

That way you have direct control, from within the script, of where you get the module(s).