(flymake-mode) how to modify the code fly-make checks

[LanX]

Hi

I wanna slightly modify the code flymake checks, are there any good
suggestions how I can _temporarily_ modify the code *before* saving?

(I know there is a AFTER-save-hook)

The motivation can be found in this article describing how a syntax
check on perl-code can execute code:

"Vulnerabilities when editing untrusted code... (Komodo)"

http://perlmonks.org/index.pl?node_id=842303

cheers
  Rolf