I am having the same issue. I made a template to a link in the footer section of an email template. Then all the emails that are currently using that template revert to draft. If I approve it, the links in the footer do not update to what the approved template has. It defeats the purpose of having a template. I now have to update manually all of the emails using that template.
If you don't want to make the change at the template level, you should be able to go in to the HTML source code at the specific email level and edit the code there. At least I've made edits that way when I've needed to add one-off components to emails.
Use the Replace HTML code