I've seen questions in the past about how to make quick changes to a uInitrd file. I hit the need to make a few changes today, and wrote a quick script others might find useful:
http://people.linaro.org/~doanac/uinitrd.py
Basically it extracts things to a temp directory, drops you into a shell where you can make changes, and then packages everything back up when you exit the shell.
YMMV
-andy