Is it ok to delete custom domain txt verification records for GitLab Pages?

After a custom domain has been verified is it ok the delete the verification txt record?

I’d suggest keeping the TXT record, if the domain needs to be re-verified for some reason in the future. There’s no security risk with keeping the TXT record - if someone tries to verify the domain to their project, a new unique verification code is generated thus requiring access to the DNS record management.