Hmmm. Again, do this at your own risk.
Begin with 4.12.2m.
It doesn't matter that you use this installation with HSFX.
Following me so far? And we begin:
BEGIN with 4.12.2m
DISABLE ALL MODS Create a folder in your jsgmemods folder called 4.12.2 Stock.
Copy Files.sfs and DT.dll into the 4.12.2 Stock folder. This "makes" a new MOD for 4.12.2m. You may now update your game to 4.13mRC4
If you wish to "downgrade" your game back to 4.12.2 to take advantage of HSFX (or whatever), ACTIVATE the 4.12.2 Stock MOD When you want to go back to 4.13mRC4, simply "disable" the 4.12.2 Stock MOD
For me, when I fly with you guys, I activate (from 4.13mRC4):
When I'm done (to get back to 4.13), I simply disable those MODS.