Hi.
You have a few options here.
1. You can add the media server to a new master server using nbemmcmd -addhost (check nbemmcmd -help -addhost
2. In the situation you described it would be better to leave this media server and if required - convert it to the Master server with the exactly the same host name
3. It would be better to replicate the Catalog Backup using MSDP and optimized duplication to another MSDP in the DR. You can sync the DR file with the information from a new dedup pool (secondary copy) with the command. Check release notes for version 7.0 and 7.1. You will find the name of the tool
Cheers,
Sebastian