seems to work.
If your previous installation was the original game do this:
1. from your existing GAAS instance: save your progress to your FB account
2. uninstall the game
3. install the GNaFF mode (see page 1)
4. if you have FB installed on your device, uninstall it
5. from the game profile menu, connect your FB account
6. the game will say something like logged in or equivalent and will ask you to restart the game so your latest profile is downloaded on your device
7. go again on the game profile menu and choose a account name (could be the same as your FB profile or a different name)
I tried on several accounts (legit, hacked) on 3 devices and it worked each time.
the only issue I noticed is that the damage multiplier doesn't work with most ship skins. The first skin does benefit from the multiplier but not other skins.
for instance, the Terminator (base ship) benefits from the multiplier, the winter terminator too, but the Mystic Terminator doesn't.
It's not a problem in itself, you shouldn't use the multiplier in PvP anyway (the game will set your wave level back to 1 if you progress through the waves too quickly)
thanks to the modder.