Unfortunately, original camera modules for N900 are quite impossible to disassembly.

Following azkay's photos, I just did a run on tearing down my faulty module (nothing to loose, as it was screwed already) - first of all, pictures doesn't match, original module looks quite differently.

Second, it's not humanly possible to disassemble it from downside and remove filter, without literally tearing it down. It's made "Chinese way" - once for eternity.

I suppose, that azkay modified it successfully on replacement module, so it's probably possible to use those. They're not original, of course, and that bring possibility of worse picture quality for normal photos - but, for NightVision, it shouldn't matter. I might give it a try, after finishing replacement body project - it might be feasible to use original module for normal photos, and modified replacement one for night vision.

/Estel

// Edit

just a wild guess, but I might have found reason, why focusing mechanism got damaged during removing module. Moving focusing lens occur due to copper spiral on moving part, which is enclosed in magnetic field of camera module's case. Actually, case contain 4 neodymium magnets, and copper spiral on lens is connected via ultra-thin wire, to module base (where matrix is located). When in use, copper ring becomes electro-magnet, and it strength is controlled by module, which result in ultra-precise control of lens distance.

Now, Using advice from this very forum, I've used shaving blade (old type) broken into two, to disable locks, that keep module in place of N900's motherboard. Such blades are heavily prone to magnetic power. It's possible, that their effect on magnetic field cause lens to move out of it's defined range, bending part of *very* delicate spring mechanism, that is part of force, controlling lens position (spring push into one side, and electromagnetic copper ring into another).
---

After tearing down whole module to pieces (literally0, I can't see anything else, that could get damaged during removal. So, again, it's a guess only, but I suspect that using non-metallic (plastic, ceramic) thin things to disable locks, should grant safe removal of module. I would avoid using anything metallic to remove it, and keep than in mind during storage (outside N900's body).

/Estel