Why didn't you join the RM in the first place?
Are your unit happy for you to go so soon after investing time and money into you?
You would have to leave the Army and join the RM and most likely carry out the full basic training. The AACC may not apply as your unit would have to put you through it and they have no benefit doing so.
Some of my info may be out of date or even a load of rubbish by now.