If you are thinking this is a way to get your third stripe, I would strongly advise you think about applying yourself to your current trade and put your efforts into getting promotion in the traditional manner.
However, if you are interested in Air Traffic Control you should be aware that ATC is undergoing a major restructuring at the moment.
You will have to complete the proscribed course at Cranwell which is a very physically challenging course.
JATCC is also very challenging, but it is only the start.
Once you are successful you will have to fully endorse at your new unit within 18 months.
If you don't achieve this, you are out.
Once you have fully endorsed, you will be subject to 6 monthly standard checks, a professional knowledge examination every 3 years and examination by the Trappers on a regular basis.
After your first tour, you will also be expected to endorse at your new unit within 3 months, or again, you are out.
Another thing to consider is, that even after all your training and examination, none of your tickets are worth anything in civvy strasse. In order for you to transfer over you would still have to complete their training from scratch.
This is very far from being some sort of easy option to getting your third up, however, if you are interested in controlling you really need to get yourself over to your local tower and having a chat with some of the boys and girls already doing the job.
Any tower will be happy to have you across and answer any questions you may have, bring biscuits.