Diamorphism already has a meaning:
https://www.merriam-webster.com/dictionary/dimorphism "the existence of two different forms (as of color or size) of a species especially in the same population. sexual dimorphism. b. : the existence of a part (such as leaves of a plant) in two different forms."
That's di-morphic. Di- means two. Dia- means across, or between. I suppose the idea is a middle style.
Unfortunate similarity to diamorphine though.
You are right. Thanks for the correction. The fact that they are so similar still makes it a bad choice though IMO.