you can't expect a user to make changes like that. To turn off the cloud lookup and to go through the locally stored list of vendors like that.
Comodo already cheks the hash of files against the Cloud to verify if they are Trusted, Unknown or Malicious. As for Digital Signatures, digitally signed Malware will most often carry a stolen certificate from a shady and relatively unknown company and almost never a certificate from a big and trustworthy company like Adobe, Google, Apple, Microsoft and others.
For me it took less than five minutes to customize the Vendor List following the guide of Cruelsister, all the user has to do is: Select all vendors, then use the search function (magnifier icon) to search for vendors the user wants to keep, uncheck those, and then press Remove to delete all other vendors.
Customizing the vendor list is more about preventing against PUPs and controversial companies like Baidu for example. As well as those Chinese vendors with unreadable characters in the list. It's more about user preference, but Comodo does prevent against PUPs and Whitelisted Malware if you set it up in the right way and it's a easy thing to accomplish. There are room for improvements regarding vendor list customization? Yes sure, and Comodo will eventually get there.