Kathan, speaking as someone who was previously involved in RAF recruiting via the UAS system, my advice is that you limit your chances of selection by far if you want "in" for only 12 years then wish to leave to pursue your "proper" career as a civilian pilot.
Why? There are many more young hopefuls out there who want to stay in the RAF for far longer. Bearing in mind the huge cost of pilot training, the RAF will understandably require maximum return on their investment. Guess who will get priority?