You cannot modify the way that Muse exports HTML in the program, but you can edit the markup it outputs however you like. Just be aware there isn't a way to import those changes.
E-mail marketing friendly output is something we are investigating, but I don't have any timeframe to offer you in regards to when it would be implemented. I'd reccomend going to the ideas tab and making your voice heard there as its a way to impact prioritization.
Cheers,
Justin