From the game install folder (~/Library/Application Support/Steam/SteamApps/common/Europa Universalis IV) I ran the following in the terminal:
find . -mtime -5 -print
This will find any files updated in the last 5 days (i.e. since I installed 1.4). This kind of thing has worked perfectly in the past for updates since the modification times of the unchanged files are not changed.
Actually, I should have used:
find . -type f -mtime -5 -print
to eliminate the folders from the output.
And once that's done, I use 'diff' to compare my files with the vanilla files. That generates a list of changes with line numbers and I can simply review the diff to see if the change is relevant to my mod...or if I want to ignore it.