All Slackware versions, including the latest v13.0, have absolutely no problems with upgrading or replacing the provided Perl with your own version. You can also install and update Perl modules as you like. The trick here is that Slackware is one of the few distributions that don't rely on Perl for getting their job done, but uses Bourne shell scripts instead (not even bash, so you can use ash or dash as /bin/sh, if you like).

Alexander