Late answer (I've been mostly away from modding since EA increased prices where I live and I stopped purchasing new packs, so I rarely check this forum anymore), but I use a simpler, and perhaps more effective, approach to detect files in need of changes, using two small programs I made and a list of which vanilla tunings my new tunings are based on.
The second program, which I run after I've updated all my mods, is the simplest; it goes through all the extracted tuning files in every mod I have, creates a clean version of the tuning in memory (by stripping all comments, ordering all attributes, and pretty-printing it to a string), compares it with a similarly cleaned version of the corresponding vanilla tuning, and creates a diff file for every such tuning inside a folder automatically created from the mod name.
The first program, which I run as soon as a new patch drops and I've extracted the vanilla tunings, does something similar to the second one, but instead of storing the diff files it compares the newly calculated difference with the one stored by the other program, and if they don't match (or if there is no previous difference stored) it opens WinMerge with the vanilla tuning in the left and my modded one in need of an update on the right (using the command line options /s /wl makes WinMerge open all files in tabs and makes the the left side file in the comparison as read-only).
Both programs also create a list of all my tunings for which they couldn't find a corresponding vanilla tuning, so I can quickly fix that issue.
This method has some advantages. Using it I usually don't even need the TDESC file to update my tunings, and it catches tuning changes that don't result in a change to the TDESC files. Also, by clearly marking my changes with comments and making sure to not introduce any unneeded change to the tuning file, finding what changed and updating each tuning file becomes very easy.
