Hi, i’m a livery creator. To make dirty is not very simple, but you can download this file ive created for a livery on flightsim.to.
If you want to all the FBW aircraft and liveries you replace the file with mine in:
C:\Users\your name\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\localcache\Packages\community\FBWaircraft\simObject\Airplane\texure
Or if you want Just for one livery, do the same things, but replace the file in livery folder (See flightsim.to link up)
Hope this helps you. If you need more help just ask! See you on a dirty plane soon!
Sincerely,
Filippo
PS.: If you want i can create a dirty livery for you, just tell me the airline company 
