TL;DR Every SSL certificate is custom at the most basic level. And beyond that, virtually nobody knows or cares.
Every SSL certicicate is "custom" in that it references the domain name, and possibly other web site/company specific data. But beyond those basics, which are, at least minimally, required, by the nature of a functioning SSL certificate, what else matters? An end-user looking at the site may notice a different color or whatever for a higher-level certification, but most people don't even notice that - or may notice but have no idea what it means. Anything else would be buried inside the details of the certificate - and almost nobody (except security professionals) looks at the details of a certificate unless the browser presents it as an error.
Personally, I've migrated wherever possible from Thawte and other high-level certificates to Let's Encrypt and nobody I know as an ordinary web user knows the difference.