If you're getting redirect loops, then something is going beyond what you've shown here. Usually, it's something like forcing "www." in one place and then non-www in another, by accident, when trying to do something like forcing https. The "other" place could be in this .htaccess, or in one in another directory.
It should be simple enough to redirect all http (non-SSL) to https (SSL) for a given domain name. I take it you have a primary domain and one or more add-on domains. There remains the possibility that you may not "see" the add-on domain names during .htaccess processing, but already have it changed to primary-domain/add-on-top-directory/. That would be seen as add-ons or subdomains being switched to SSL, even though you only specified the primary domain in the rules. Anyway, something to keep in mind (you might have to specifically exclude the top level directory of the add-on or subdomain in a RewriteCond).
My understanding is that subdomains are strictly local to Lunarpages' internal nameservers, and have nothing to do with a registrar. Add-ons are registered with a registrar, which can be LP (handled by Tucows) or some other registrar service. Both come in to your site under the primary domain, with a specified root directory (public_html/addOnName/ or public_html/subDomainName/), unless something has radically changed since I last played with this. If you attempt to put a subdomain on an add-on domain, I'm not sure what will happen (didn't work years ago).
Anyway, you need to use cPanel/LPCP/other control panel to add or delete add-on domains or subdomains, but be careful about getting tricky with it -- things like subdomains on add-on domains may still break. And there's always the possibility that SSL doesn't yet work on some things.