I'm not familiar with the differences between the XZ models (I'm on a Sammy GS2 atm). But the fact that crossflashing works for the XZ, doesn't mean it will work for the XZ1; for example, I can't flash i9100g ROMs on my GS2, because even though they are the same model, the internals are different (though the GS2 example is an extreme case).
Of course you are free to try crossflashing the C6902/C6903. Perhaps you won't break much, but you'll probably won't have a working radio (in other words: no calls, no texts, no data). Or you might brick the device entirely.
Personally, with such an expensive device as the XZ1, I wouldn't risk it and stick to C6902 ROMs until we (=the community) know more about the devices.