Change template of an email send once built it?

Hi everyone,

I was wondering if it is possible to change the template an email uses once it has been built out and approved? It might not be "live", i.e. part of any actual sends, but wanted to know if it's possible? If an email uses Template A, and we would rather it use Template B, is it possible to change it? Or would you have to build out a new email using Template B?

Thank you!