I think a combination of 'diff -c' and 'patch' would work if doing an update on regular basis.A script with only the files we know were enhanced for these features would reduce the output to validate visually.
From 2.0.1 to 2.6/7 would likely be a more manual effort. But then again many of the files have only relatively minor changes per release.
The first thing I would love to know/hear about is how Glade was set up for this effort.
In my opinion maintaining PP updates after mod is nearly impossible. I had to freeze updates afterwards. Changes between updates can be huge - new or changed files, new machines, complete system loading rebuild and new LinuxCNC compilation files.
I can live without it anyway.
I tried teh method you mentioned and it did not work. I have yet to see a working example of a PathPilot Screen mod where things like adding a new button were done.
TP 
