Although I've not had much success with importing BCHs into PM ORAS maps, to my knowledge the only way to do this r/n is using the tools from the official SDK, NintendoWare/NW4C in particular.
You'll have to get your new/edited model converted to CRES (not BCRES! The only difference between these is that CRES is an intermediate XML format for the binary BCRES(aka CGFX))(I'm pretty sure other tools from the NW4C can be used to accomplish this, I just don't remember how I did it), then use NW4C_h3dbincvtr to convert your CRES to BCH...
Honestly, I dunno if this will work for you or if it won't, IIRC my experiments didn't work because I either messed something up at the editing stage, or because the BCH version produced by the h3dbincvtr I have didn't match what the game uses.
Footnote: I'm not aware of any romhacking utilities that can export BCH at the moment, sure thing Ohana-3DS and SPICA can import and view them, but exporting isn't really a thing, so you'll probably have to stick with SDK utilities for this (unless there's been some new thing I've not heard of).