If you want to keep your sites as one-click installs, then yes, unfortunately you will need to create new one-click installs for the new domains or subdomains, and then manually copy over their data from the /wp-content directories of your previous installs (or you can export those things with a plugin like you mentioned), and edit the new wp-config.php files (in the new installs) to point to your previous databases. Then adjust URL settings for each from the database or wp settings.
if you'd be ok using WP's auto-update settings instead and not having them as one-clicks, I'd suggest simply hosting the new subdomains on the same users as the current installs, and point them to the same directories. Then log into /wp-admin on the older installs, and change URL settings. You Might need to do some cleanup (via search+replace in phpmyadmin) in the database after for any old urls saved anywhere, but it would be less work.
Let us know if you have any more questions!