How to emerge packages with config changes

[vert]

I want to install ghostscript with additional printer drivers (well, in fact only one ), but to do that I need to alter the Makefile.
If I do that and replace the original tar.bz file emerge complains about the message digest not being the same (and for good reason of course). Is there a way to skip that check or should I proceed in a (very?) different way ?
I could of course try building a complete new ebuild file, but that will probably cost me a little too much time at the moment.
thnx for any suggestions

[lunatc]

Try do do an

[vert]

that worked... kinda
at least it would compile with the changed Makefile
but it didn't solve my problem (the printerdriver is still not included)
no idea why