In TLCstuck, John beat Caliborn down until he died and placed him on his Quest Bed where he became the Muse of Space; in short, god-tiered into Calliope. Is that possible in canon?

It’s likely not possible anymore because Caliborn predominated- The moment his cheeks filled in, every part of Calliope was gone from him. That’s why Roxy calling out her name didn’t wake Caliborn up as Calliope anymore. She’s gone from him.

Also in any case he’d need to be put on Calliope’s Quest Bed, which doesn’t exactly exist in Caliborn’s Session.