You're updating the version of Perl, not the scripts, and asking what doing so may break, right?

You could run through all of the perldelta POD's to scan for problems. Or you could install the latest Perl in a different path, retaining the older version too, so that you can freely go back and forth as necessary.

This approach will allow you to thoroughly test the old scripts under the new Perl versions. It's impossible for us to know what version-specific things are being used in the scripts you are talking about, without spending a lot of time looking at them and researching.