Creating an ext 2 image update

[Arthur Rodrigo Sawazachi Valadares <arthursv linux vnet ibm com>]

Hi, I tried following the instructions from this link:
http://fedoraproject.org/wiki/Anaconda/Updates#Compressed_ext2_filesystem_image

But I don't think I understood it right. I want to change just one file,
yuminstall.py, how do I do it? I tried dropping the yuminstall.py in the
mounted directory of the image as instructed, but when the installation
starts (after setting up network), it crashes because it doesn't find
the file's imports. The image is 1.4MB, how could I put all the imports
(200MB) in it? I just wanted to replace the original yuminstall.py by my
own modified version.

Sorry if it is a dumb question, but I couldn't figure it out :/

Arthur V.