You would need a program like Unreal Unpacker (or whatever the name or equivalent), export the model into another program, one that supports 3d model editing, edit it (obviously), save and export the 'new' model, and yet another program to overwrite in Bio; or even have to unpack and repack the entire Bio build. IF that's even possible.
I've seen it said here that either it isn't, due to the way they package and finalize the builds... or if possible to figure out a workaround, it would end up costing more than it's worth because you'd need a bunch of different programs and obviously need to know what you're doing with them.
It could be possible... but between both takes, no one's done extensive modding like that yet, sadly.