Not afraid to use someone else’s FM file (or tweak it myself) for certain circumstances. Not to make a plane into a P-51 Mustang but to suit it into my idea of history (different engine sizes for the Spads for example) or just to make a plane easier to fly with a joystick and keyboard like the turn ability (nose rise not rate) of the Fokker Dr.1

In going over the work of the FM modders I see everyone seems to change a different *number* of file and file folders. For example some change the .xfm file in just the aircrafts main folder. Some the main folder and the QC one. Some include all the Squadron folders also.

Why the difference?
If I just need “my plane” changed (like the Dr.1) what folder .xfm files need changing? Just the main one?
If I need all changed (like making all Spad VII’s the 150 HP version) which file/folders then?