According to my Subaru Service Manual the harness and connectors to the heated mirror are different form the non-heated one, but it is impossible in the manual, based on how it is written, to know if there are any other differences and what any of them look like. An if there are, they will be internal rather than external and associated with the harnesses one would think. The mirror glass itself should be interchangeable, given how the mirror itself is made and mounted.
The other option is to find a heated mirror assembly that meets your budget.
Like maybe from here:
https://www.lkqonline.com/
The other option is to find a heated mirror assembly that meets your budget.
Like maybe from here:
https://www.lkqonline.com/