If the MFT update is anything like other software updates, it will do a check to see what is installed already and proceed to update the already installed files. If you have files it diesnt recognize, it will killtge update process before beginning and throw an error. Again, IF MS created this like virtually all software.
The size of the update merely reflects that is a cumulative update (ie, able to update all versions of MFT).
If the update truly doesn't work on all cars, chances are it won't install.
2012 Ford Focus 5dr Hatchback Metallic Black SEL 301A