mmm...
Obviously it doesn't work this easily, sadly.
If I try and create an ice texture for the uboat, it simply won't appear ingame. For example, taking Uboat7A_deck.dds, replicate the texture adding some ice on it and renaming it Uboat7A_deck_ice.dds to mimic the file structure for other boats simply don't work and won't show anything.
Apparently, there's some kind of trigger linked to the time period of the year that makes it so the textures switches to their _ice.dds counterpart, but apparently, it won't do so for any textures of any sea object as if it was just checking for the _ice suffix.
Can't find such a trigger anywhere under goblin and GR2 files, I fear it may be hard-coded... TDW, any thoughts maybe?
I'd be interesting in knowing just how the game knows which textures to use for each given 3d model, as it may be there. Hexediting GR2 files maybe...