Hi Dan,
I understand that you added a custom domain to your account, and you want to add some A records for the domain from the portal site.
Under this situation, I suggest you try to troubleshoot the domain from the portal site. Login in to portal site, and go to domain management page, click the domain, and click Troubleshoot. There will appear a wizard which you can go through. If there any error promotes, please capture the error message and post back.
In addition, for a further troubleshoot, could you please provide two screen shoot and the custom domain name?
1.The domain status, you can get it from the steps: Login portal site, choose Admin tab, under Management choose Domains.
2.Another is about the partially redelegated message.
I will send you a private message, you can reply to it to provide the information.
For how to read and send private messages, you can follow the steps as below:
•Go to the Your details section on the right side of the community site.
•Click Private messages.
•Click the subject title of the response to read the message.
•You can reply by using the form in this display.
•Click Submit Reply.