Can I add custom email domains to blocklist in the global form validation rule?

Hello! Marketo Engage has a prebuilt global form validation rule called “Consumer Email Domain Blocklist” that I'd like to activate. In addition to the domains listed in this prebuilt rule, I'd like to add more custom email domains to also blocklist. The challenge with this is - it seems I'm not able to add more domains to the prebuilt rule. I also tried creating a new global form validation rule to add all the email domains I want blocklisted but there's a 2000 limit. I also tried distributing all the email domains across multiple global form validation rules and activating them but Marketo flagged that I can only have one rule active at once.

Any suggestions on how I can blocklist more email domains in the global form validation rule?