If you have not been sworn in yet, then you should consider requesting the new trade NOW. To go from infantry to medic requires a higher score on the aptitude test, although the physical/medic requirements are not as strenuous. If you're sworn in already, you will probably have to re-write the test in addition to doing another interview with the PSO (personnel selection officer). If you're already in and have started training, then you are occupying a position from your unit. If, after the completion of your BMQ you mention a remuster, they will probably not be too pleased as they will have just wasted one of their BMQ positions on you when you KNEW you had no intention of staying, and as such will probably be more reluctant to process your remuster quickly. So, if you're not sworn in yet, go for the new trade right away. If you are sworn in, get the paperwork started well before you do your BMQ. It will probably save you a lot of time and heartache in the long run.