Malcolm Beattie's B module allows you to examine the Perl op tree at
runtime, in Perl space; it's the basis of the Perl compiler. But what it
doesn't let you do is manipulate that op tree: it won't let you create
new ops, or modify old ones. Now you can.

Well, if you're intimately familiar with Perl's internals, you can.

WWW: http://search.cpan.org/dist/B-Generate/