No - reverting from X2a back to X2 involves more than just renaming the sonarpdr.exe file.
There are other inter-connected changes to other components.
In my opinion, the best way to go back to X2 would be to completely uninstall X2a, including removal of roaming data, registry keys, and such - there have been other threads that cover the exact process of doing this - I believe Britol_Jonesey has put them up a few times.
After the complete removal of all things X2a (no need to remove plugins and that sort of thing, I am only speaking of the main program), install X2, and you should be fine.
Bob Bone