packaging, modify a patched package

[Mihamina Rakotomandimby (R12y)]

Hi all
when I download and extract the source of a package, I mostly find 
patches in it.
It's OK.
But know, I want to modifiy those packages to fit my needs:
What is the process to follow in these case?

-- 
Chef de projet chez Vectoris
http://www.google.com/search?q=mihamina+rakotomandimby
System: xUbuntu 8.10 with almost all from package install