Technically they could.
They could do the same thing I do and use
You must be registered to see the links
to see the differences in different versions and what the difference is with their mod installed and or the previous version with the mod installed. From that it becomes nothing more than using the tool to merge which ever direction they need to do.
Then they compare the new version to the base version and copy just those files out that are different.
The first thing they need to do before doing that though is. Go to every file in their mod and bug fix and change the line endings all to "\r\n" other wise every single file is going to show it is different. It's real easy to fix this issue using
You must be registered to see the links
it can change that type of thing in every file in every directory and they can specify just to search rpy files.
The only real issue is when there are a lot of bugs on Vren's part like this last update. If they want to know where all those problems are they could download my mod compare it to the base using the winmerge mentioned above and thus find out where most those are. How they choose to deal with them is up to them but at least they wouldn't have to find them by playing it.