Unfortunately JP the RAF policy on pilots doesn't include letting them choose which direction they wish to pursue their carrer in.
By all means apply for a change but expect to be asked 'Why not fast jet' and don't expect to head off to a multi training unit (starts with Jetstreams at Cranners, I don't count the lead-in training on the Firefly as anything more than hours building) just cos that's what you would like.
Especially as the RAF is leaking fast jet pilots like a sieve and that's where they need to recruit.
But never tried never gained