Hi @goboldfish. Welcome to GoDaddy Community!
You can definitely use a UCC SSL Certificate to cover multiple subdomains. Wildcards are better for when you have a large number of subdomains you need to protect. However, there's no way to change an SSL Certificate from one type to another. You would need to purchase and request a new UCC certificate in order to replace your wildcard. Hope that helps!
The SAN can protect multiple domains, and subdomains. 'Subject Alternate Names', many different sites. A Wildcard SSL will protect ONLY that domain and ALL subdomains of that specific domain. So if you are wanting to protect yoursite.com, store.yoursite.com, shop.yoursite.com, dev.yoursite.com etc.. a Wildcard would work well.
If you wanted to protect yoursite.com, anothersite.com, differentsite.com, runningoutofideasforsitenames.com etc.. Then the SAN needs to be implemented. Hope that makes sense.