When would Templater do this? Templater can’t trigger when you manually insert text onto the main note. Maybe for that kind of action you could use Linter plugin, to verify that links in frontmatter exists, and create it not.
Another option, but I’m not sure how achievable the is, that you could use Templater to create all new files, and then backtrack where the link is found in the originating file to see that this is an author link, and then select the author template.
I believe the most common method would be to insert the link using Templater based on some suggester indicating this is to be an author link. Or possibly to have a fully qualified link into an authors folder, and then use folder templates.
In other words, it all comes down to what’s your workflow and how do unsert that author property in the first place.