Just a small blog post about a small requirement I needed to be sure of that worked.
While creating an email message in EXM, you can use replacement tokens like $fullname$. You can read more about it on this Sitecore document page: Insert a token in a message
Some of our clients use the import HTML functionality to send out premade emails and wanted to use tokens too. And this is no problem!
Just add the token to the html before importing it in EXM.

Sidenote: the drawback of importing HTML is that you can't change the contents of the mail. Unless you make use of a placeholder so you are still able to add renderings.