Is there a way to edit a .pkg?

[bf2loser]

I was wondering if theres a way I can remove certain files from a .pkg and then insert my own. Specifically I'm talking about removing the appleintelthermalmanagement.kext or whatever its called from the 10.5.3 update and then inserting ps2 support kexts. So far i've only found out how to copy files that are in a package to the desktop, but I haven't figured out how to delete them from the package file