Anything's possible, given the talent. Replacing the scales on an all screw construction knife that has full liners is the easiest, anything beyond that is harder.
The original FRN C41 Native Lightweight uses a 1 piece FRN handle. At the very least, replacing it means not only making new scales, but also making a replacement backspacer. Depending on what you choose for scales, and whether or not you want to be able to mount a clip and have it stay mounted, you may also want to consider making liners. Then you have to figure a way to put things back together. It can be done, but it takes a fair amount of talent. This started out as an all pinned FRN Atlantic Salt. Now, thanks to a very talented customizer, it has birdseye maple scales over titanium liners and a matching ti backspacer.
The FRN Native 5 is all screw construction so it would be easier, but I'm not sure if the handle is 3 piece, with a separate backspacer, or two piece, in which case you'd still may need to fabricate a backspacer.
Manix Lightweight has a 3 peice handle, but it's all pins, except for the pivot, so new hardware at the very least. The ball lock carrier may also be inletted into the handles, so you may need to mill pockets for it in the scales.
None, IMHO, are projects for the faint of heart.