I guess the title is the question, is space polymorphic? Or is it a background on which things occur?

Google search defines polymorphic as a term used by biologists. What do you have in mind?

Using dictionary.com I found this under polymorphous

 

1 - "having, assuming, or passing through many or various forms, stages, or the like."

2 - "polymorphic"

 

So I mean probably "passing through many or various forms, stages, or the like".

 

As opposed to a background through which things pass.

That doesn't particularly make much sense. Space being a volume.

 

However if your referring to the thermodynamic conditions of the Universe. Then it has undergone several stages.

Example particles dropping out of thermal equilibrium, which affect the dynamics