Migration Update: Custom Domain Issues Affecting Email Sends

In the midst of a migration from another platform. Starting slowly. Sending ~500 daily from a list of more than 40K. Today was first day under our custom domain, which was entered on Friday. The DNS wasn't fully completed and some of today's recipients weren't able to open links. The people who couldn't were those being sent the new domain on the smart warming phase in. Not sure we are going to resolve the issue before tomorrow morning's send. We have a ticket into support, but wondering if there was a way to send under beehive's domains (as I was during the trial) until the domain issue is resolved. If so, how do I do so?