Hey @John Furgurson58! It isn't possible to set this up to happen automatically right now (but please feel free to file this as a feature suggestion here52), but if you navigate to the list of subscribers who have opened your email, you can tag them manually using a bulk action48.
To navigate to the list of openers for a broadcast, click into the broadcast from the broadcasts page42 and then click 'Opens' from the sidebar.
For sequence, click into the sequence from the sequences page38, click 'Reports' from the top of the page, click into the individual email, then click 'Opens' from the sidebar.
I hope that helps! ☺️