I have an upcoming trip with KLM, and have entered my Flying Blue number into the booking. I would like to switch to Virgin Flying Club as I have a reasonable balance in there, and would be more likely to use VS for a future redemption. There are also 3 other pax on the booking that I made, one is my wife who'd probably also like the VS miles (she just doesn't know it yet). It seems that once you enter FF details, you can't change them as the box is greyed out. It's not a huge amount of miles from a cheap BHX-AMS return, but I'd hate to waste them. Is there a trick to change this?