Thanks for the clarification and apologies for the noob question that follows.
But, what exactly does an RIL Mod do? Why is it required? What happens if I flash just the radio and not the RIL?
Again read my short explanation in post #14
. RIL is sort of like the "driver" for the radio that's being used by the OS.
Each ROM has it own RIL drivers associated with the radio that the ROM shipped with. Usually when you use a new radio it's a good idea to use the RIL from it too as it may improve the performance of that radio. You didn't need a RIL up until now because you used radios that were shipped with the official 2.09 ROM, but this latest radio is from 2.14 (i think) CHT (or HK i dunno exactly) ROM. So what the OP did is based on the files from this post
and made a diff to add the ones that needed to be for MCR ROM (as the one from the XDA post is for OpenDesire).
You don't NEED to use the RILs for the new radio to work as the existing RIL driver can communicate with the radio just fine, but some say that using the updated RIL improves GPS lock time or improves 720p camera. It's all subjective and only you can be the judge if it improves something or not. So far with this RIL mod nobody complained about any bugs so it's safe to try it (with the XDA mod for OpenDesire though people were complaining the phone lost signal after a few minutes of booting up, this does not happen with this the MCR mod).