TreExplorer has a semi decent hex editor already built in, luckily. Just make sure you highlight and paste over that, instead of just pasting it in, otherwise it'll overwrite other data, look here:
CPAP = .prt (Particle) link chunk
PSND = .snd (sound) link chunk.
All the .cef (Literally: ClientEffect), does is link 'effect' files together, so like a particle and a sound, etc.
The object .iff is just the base file for an item, it makes it easy sometimes to just use that because it automatically gets and sets all needed file links (if they're in preCU, otherwise you'd need to find and export everything it links to) through just one file.
You can replace just a model (and it's shaders, again if it's preCU you just need one file, otherwise you need the whole chain) by using the .sat (if it has a skeleton/is 'morphable', like clothing) or .apt (same as .sat, just without the skeleton, like a weapon or some other static object).
Just a quick general run down:
.lod files = Level of Detail container for static models (.apt files link to these)
.lmg files = LoD container for files with skeletons or that use other skeletons (.sat files link to these)
.msh files = Static mesh
.mgn files = mesh with skeleton
.sht files = 'Shader' links to the .dds (texture) and the needed actual shader (.eft)
.eft files = 'Effect' files link to the actual HLSL shaders (.vsh (vertex shader), .psh (pixel shader)).
So, if you swap the .cef, you'd just get an effect swap, easiest would be, if you want just the model from the BF, grab the (you can see this if you look through the chunks of the object .iff, you'll stumble across an XXXX chunk that has 'appearanceFilename' inside of it, this will give ya the name. Now, this seems to just link to 'wp_pistol_dl44_combined.apt', which appears to be a preCU model, so that'll be easy. Simply rename whatever file is linked inside the appearanceFilenameto 'wp_pistol_dl44_combined'.
P.S. I just saw that if you open the .toc that loads all files at once, including NGE, it already links to 'combined', because it's a CU item. The PreCU has just 'wp_pistol_dl44", try to see if using the preCU object iff works, then you won't have to edit anything, if it crashes, you'd have too look for the preCU dl44 in the .tre files manually and grab that.
But here is the preCU one, just in case: https://mega.co.nz/#!8lJzDK4J!lShSpuPGzbQP_EhdOqAp_k74PbfQrAIE6GQOl6fj6Y0
You just need to edit the appearance XXXX chunk, remember, copy and paste over selected stuff, don't start writing inside it or it'll overwrite other stuf.