Well the "proper" way that you would create a player head mod for the PC version involves editing appearance.2da, heads.2da, and portraits.2da (in addition to the head model and textures, but you can use the vanilla ones for Bastila). I have no idea what the deal is with Xbox 2DAs, whether there is some big endian/little endian thing going on. You could try going that route first, although it would require extracting them from a BIF, presumably. If the Xbox data is anything like the PC, they should be in a file called 2DA.bif. You could try copying that and the KEY file (probably chitin.key) to your PC, then extracting it with unkeybif.exe from Xoreos Tools. Then you could use convert2da.exe to convert the required 2DAs to CSV. Then you would follow any standard "adding a player head" type tutorial to add the new data, then use convert2da again to convert the CSVs back to 2DAs. Then you'd transfer the modified 2DAs back to the Xbox, putting them in the Override folder. Like I said though, I don't know if Xbox 2DAs are different from PC 2DAs, so I have no idea if that will work.
Assuming that doesn't work, the other option is the more brute force route, replacing one of the existing player head models with the Bastila head model (P_BastilaH). This will require changing the Odyssey Base name, the quickest route being to decompile, edit the ASCII model, then recompile. MDLEdit can handle Xbox models, so that should be fine, although you'd presumably want the Xbox supermodel (P_BastilaBB). Those should also be in a BIF file. You'd also need the Bastila head textures, which are in ERFs on the PC version, not sure for the Xbox version. I'd suggest trying the 2DA route first though and seeing if that works.