The easiest thing to do is install Perlbrew. It is Linux/Unix specific, and uses BASH. If you use Zsh or Kornshell, you need to munge the scripts a wee bit. If you're on Windows, well... good luck.
Perlbrew will allow you to install multiple versions of Perl as user installed Perls. You don't need root permission to use these various versions of Perl You can also run CPAN via Perlbrew to install modules in the various versions of Perl. This is a great way to install multiple versions of Perl for testing purposes. My default Perl is 5.16, so I've installed 5.18 to get the latest, 5.10, 5.12, and 5.8.9 to match as closely as possible the version of Perl we run on our RHEL servers.
To switch from one version of Perl to another, you use this command:
$ perlbrew use 5.10 # Use this version in the current shell
or
$ perlbrew switch 5.10 # This is now your default version of Perl
To install a particular version of Perl:
$ perlbrew install 5.10 # I'm installing Perl 5.10!
Perlbrew uses $PATH
to set your Perl version, so you need to be careful with your shebang. You're not necessarily running Perl under /usr/bin/perl
anymore. You shebang in your Perl scripts should be:
#! /usr/bin/env perl
Way easier than attempting to downgrade your default installed Perl.