To answer my own question...
I changed the CDA for Taiwan, to the one for India. Connected the phone to PC Companion with the intention of "repairing" it.
But viola! PCC reported that an update was available. That turned out to be the .510 for India (I was on .510 for Taiwan).
Best part is, all my apps and settings are intact.
So, for those who want to try out firmware from other regions (mainly for the region specific apps Sony has bundled):
1] Root the phone, change the CDA entries in the build.prop file, which is in the system folder.
2] Reboot the phone, connect it to PC Companion, and Search for Update. Even if the version is same, PCC will treat the new region's firmware as an "update".
3] Note that you will lose root access, There is a "kernel swapping" method mentioned here to root the phone again: http://forum.xda-developers.com/show...&postcount=389
This worked for me. the Vroot and 360 methods did not.