An official guide has been posted to port it.
So if your phone support minimum configuration & CM10 build available for it, then you can port it. Now most of the Xperia devices have problem with the amount of internal memory. If your devices has at least 4GB internal memory (not only intenal memory, you need to specifically check the amount of
/system patition) you can proceed. Also check, related XDA forum to know about developments (if any)
various Devs are working on porting, you can check the list from here https://wiki.ubuntu.com/Touch/Devices
Currently, only Xperia S & T are listed.
Now you are asking about mixing CM9 with CM10. I don't know whether it is impossible. It may be possible, but will be damn difficult for sure. CM9 to CM10 is not just about replacing files. I would suggest to go to CM forum about this question. The question has nothing to do with ubuntu.
Ubuntu only uses the base drivers & io level code of CM10, so that developers can use existing drivers (which are proprietary).