I have explained what is involved to do Domain split over here:
https://vox.veritas.com/t5/NetBackup/Modify-images-in-order-to-point-new-master-server/td-p/873679What you want to accomplish is called a domain split.
Only trained catman consultants can do this.
Even to an experienced consultant, domain split is the most complex catalog manipulation and requires a lot of pre-work.
You firstly need to group the media servers with their clients - all clients that will move to the new master server, will need to ONLY backup to the media servers that will move to the new master server.
All clients that will stay with old master server, must only backup to media servers that will stay behind.
Something like this:
Group1: Client1, Client2, Client3, ClientX, ClientZ - will stay in existing environment on Media1 Media2 Media3.
Group2: Client4, Client5, ClientY, etc will move with Media4 Media5 Media6 to new master.
List images for clients in Group1 that reside on media servers that will be in Group2. (bpimmedia )
Duplicate those images to Group1 media servers. Expire images on Group2 media servers.
Do the same for Group2 clients.
You need a good knowledge of NBU commands such as bpimmedia, bpduplicate and bpexpdate as mistakes can be costly and cannot be reversed.
You also need to ensure that there is sufficient space on Appliances.
You should not duplicate (or backup) images for 1 client to more than one Appliance - you lose global dedupe if images reside on multiple media servers.
The steps above is not part of a standard catman engagement, but if you engage with an experienced consultant, they may add additional consulting hours to assist.
Once the clients are split along media servers, your environment is ready for domain split using catman tools.
The catman tools will transfer images, and other DBs from Master1 to Master2 and perform that database name change on Master2.
Group1 media servers is then removed from Master2 and the same for Master1.
If you do it any other way, you will have no support from Veritas.
Domain split is also part of this Article:
DOCUMENTATION: How to migrate the NetBackup catalog information from one platform to another (UNIX to Windows or vice versa), rename a Master Server, cluster an existing Master Server, or merge multiple NetBackup domains.
http://www.veritas.com/docs/000026956