I did make some tutorials for an older version but theres so much to cover it would take me a lot of time. Time that I do not have much of and with very little gain. I did however add some explanations to some of the files in FMT.
If a Live Tuning occurs. Delete the attribdb.bin at C:\Users\{your user name}\AppData\Local\Temp\EA SPORTS FC 25\onlinecache0 . FMT will do this automatically.
UI modding is very difficult in FIFA/FC because they use this horrible system of custom json, XML & heavily customized SWF. Its 100% doable but not as easy as other games