If you pass the SVA as a newly built car then you will be issued a plate related to the date when the car was presented for registration. ie a late 2007 car will get a 57 plate (I think). If you are unlucky enough to get a Q plate then there is no way of changing that
However if you get a plate that is not a "Q" you can buy a plate that looks older and have that applied to the car - you just can't make the car look younger than it's 1st registration date. I hope that helps a bit.