I remember in the first Bard's College quest one of the options was to make up a story aout Olaf One-Eye being the dragon Numinex in human form. I've always found the possibility of dragons masquerading as men fascinating, so I'm wondering - are there any occurences of dragons taking on human form in lore? Not counting the Dragonborn, of course. I'm looking for more of a form-swapping ability, perhaps using illusion or alteration magic?

Not that I'm aware of, other than a select quote by M'aiq.

Some of the theories that bounced out of 'Ysgramor is a Dragon' are relevant to this too, where people chose to take it literally, either granting dragons the ability to shapeshift, or granting Dragonborns the ability to take the shapes of dragons.

Certainly an interesting hypothesis. Since dragons are the children of Akatosh, and thus related to the Aedra, do they have a fixed form as well?