Anytime you repot or mount something that's in bud or flowering, you risk doing root damage that'll make the plant drop its blooms. Doesn't mean it can't be done successfully if you're careful and don't expose roots that were submerged to the open air. If there's no big hurry though, and you want to enjoy the flowers as long as possible, I'd just wait. On the other hand, if new roots are starting to emerge and you want to give the plant a good start on its mount--especially if you've already seen the flowers--you might as well cut the spike and mount the plant. It's what I would do if it were me.....