For a rebuilt master server, the IP address is not critical. The name must match on a rebuilt server.
Now, if you actually want some help, you will need to provide some more information. Such as
What has happened?What are you tryin...
That sucks about the backwards compatibility of LTO8 (before then of course it could read 2 generations back). Anyway I digress.
If the new NetBackup master has the same name (and platform type) as the old master, then you could d...
If you don't have working DNS then yes you would need to update the /etc/hosts file. To change the IP of the master, the file to update is typically /etc/sysconfig/network-scripts/ifcfg-<interface>.
As long as all your clients and media servers can resolve the new IP address it will be fine (and if you use DNS then this should be straight forward). You may need to use the "bpclntcmd -clear_host_cache" command on some clients to clea...