It it ain't broke, don't fix it. The reason for those modules might have been that they were used by other scripts: perhaps they never got written, or they faded away, or you are not aware of them.

But... using || die instead of or die after two-arg open statements might be broke depending on parentheses.

You did not mention use warnings; and use strict;. A lot of older code did not bother with these, so if you are looking for bugs that might be a place to start. It might also help rooting out pesky package variables.

When tasked with learning a system like this in the past I started by writing documentation for everything. That way your work may benefit others, and you will have something to show Management for the time you spent.