so, this is what i propose. Extract the bsa with FOMM, import it to blender, export it as .3ds, open it in 3ds max, edit it, travel back up the chain. This'll work right? After i get it back to a NIF file, how do i get it into Fo3?
I can't import the Nif directly into the 3ds max because it's v13 and i can't get any working plugins for it. Unless someone can give me the link to one

You'll lose some of the data specific to nif files as 3ds won't store it, so it probably won't work.

skip the blender/3ds part. and just import it straight into max.

Why not use the niftools plugin?

It would work yes. Not 100% but it would work. But yeah, why wouldn't you just import the nif? Saves time, money, and frustration.

if your just going to change the mesh, and if its just a simple model that is not attached to any bone structure [armor and body parts] you can also just export it from nifskope as an obj. or 3ds file and import it back into nifskope once yer done editing it. You can change armor or combine various armor meshes by copying and pasting the nitrishape? branches and pasting them in another nif file. You can also change armor meshes by pulling and pushing vertex [let's say if you want to make an armor look more buff or skinny or fat for example] as long as you don't add or remove any vertex it'll show up ingame. But why would you want to do this? if you have blender or max you can easily export it from there into a new nif?