I don't recall anyone ever doing this IC. The only one I really remember was Padwei going from human to storm giant.

I wonder if instead of going full class changes, could Imms remove and add skills to make people into a hybrid, one which naturally would not be as good as a pure version of either.

I always liked the ides of hybrid classes, but I think the coding work would be far far too much to implement. A Primary class and a secondary. Primary gets skills to maybe 40/45, lose some of the class defining skills though, and secondary adds maybe 5 low/middle tier skills from the class, with the same caveat. Course everyone would choose healer or bard as secondary for the buffs.