Am due to start Basic Training begining of April, going In as a VM but would now like to go In Royal Engineers. A mate who's serving said quite a few of his mates managed to rebadge by asking In basic.. What's the likelyhood of me being able to do this?

Cheers, Butch.
Better now than later Butch.

By the time your first tour is done and you've tarted up your pit space to a good standard you probably won't bother. I re-badged after a few months off and it wasnt my best move.

Dig around though and try and get a healthy insight into your preferred choice as you'll probably hit a brick wall if you want to move again .
Just been told I can't transfer at the end of basic and If I really want to go In Royal engineers I'll need to wait for another basic date..

Ooops! Is that likely to be a long way off then?
To start with congratulations on getting selected to join. If you're not 100 percent convinced or feel you got mis-sold (...don't worry get in now and change later etc) being a VM, although you should have signed to say you were happy with your choice, then you need to raise it early in training on your initial interview with your Troop Commander. If the trade you're going into isn't critical, then changes are subject to the losing and receiving capbadges agreeing so the quicker you raise it the more time you have to resolve it subject to you knowing what you want to change to. Bottom line is it's your career so ensure it's what you want to do. Your troop staff are there to help you so ask them, if they don't know they can get someone who does.
You sign a JOB OFFER letter which was introduced 6th April 2010 that states that the job you are accepting is the job you want and are not permitted to change once in, this is to stop wastage of money that has accured for years on soldiers changing once trained. There will be some circumstances where the Army can change you if they need to due to cut backs in trades but on the whole ensure that you pick the job you want to do for the next 12/24 years.