To be able to move plants from veg to bloom you just have to make sure of 3 things:
1) The roots do not get tangled with each other or equipment while they are growing. Many NFT settups do not take this into consideration, since the designer made the thing to use throughout the entire life cycle. Here's where one advantage of DIY comes in.
2) The openings that the net pot sets in are the same size for veg and bloom.
3) Allow a little more room for the roots to grow in the bloom area, since they will of course grow bigger than in the veg area.

My NFT rebuild includes seperate secondary reseviours for each plant. One advantage of this is there is no way roots can become entangled. Occasionally I'll loose a few root strands on some fittings in the chamber when I pull the plant out, but it's no biggie. The plants don't seem to object too much.