[obloquy]

It's a tempting concept, but Tolkien never gave any more detail than discarnate, "clothed", and incarnate. There's every indication that the final incarnate stage of an eala is the same corporeal state that the Children are born in. The differences in hroa that you describe would not be out of place in the "clothed" category, but the Istari, Melian, Sauron, and Morgoth (our concrete examples of fully incarnate ealar) all apparently ended up exactly like the Children. They could no longer conceal their evil through manipulation of their hroar (in Sauron's and Morgoth's cases), and they were powerless without hroar. Shapeshifting doesn't seem to be possible for any incarnate being, regardless of original nature. If a Balrog changed shape, he must have been merely "clothed" and not incarnate; but if he was only deprived of a physical raiment rather than truly slain, then Gandalf's sacrifice was vanity.

(I have not forgotten about Beorn, but he is somewhat anomalous, at least as mysterious as Tom Bombadil, if not more. Additionally, he comes from a time when Tolkien's concept of embodied spirits did not include a "clothed" provision, and were either discarnate or incarnate.)