Hello contra-sh, and welcome to the Monastery!

I’ll just address one part of your question:

Seems like the override only works when I call the function. That's weird because I modified the value before including the logging module.

No you didn’t! use logging; is the same as BEGIN { require Module; }, which means that the code in “logging.pm” is loaded and run before the rest of the script begins running (because anything in a BEGIN block is run at compile time). Change that line in “run-unit-tests.pl” to require logging; and the output is:

23:48 >perl 1030_SoPW.pl
Import...
VAR1 : [override1]
VAR2 : [override2]
Running function...
VAR1 : [override1]
VAR2 : [override2]

23:48 >
[download]

- Should I see any difference if I use require instead of use?

Yes! (as just explained).

Hope that helps,