making changes to etex

Hello everyone,

Maybe this is a strange question - but I'll ask it anyhow as I couldn't 
really find any documentation on things like this.

I've been making some changes to tex.ch as an experiment. Now, however, 
pdfetex fails to build because it tries to apply tex.ch to the 
pdftex.web (I think). Can anyone enlighten me on how one is supposed to 
make patches to etex?

Thanks,
johannes