Working with a bunch of VMs, I often have to change names, IP addresses, etc. Today I finally got tired of having an extra (non-functioning) entry in my DB2 control center because I changed the hostname of one of my DB2 servers. Happily, I found this great entry on how to do it:
However, after going through the steps, you need to restart your database administration server service, named DB2DAS - DB2DAS00. Once you do that, your new hostname appears, and the default instance (named DB2) is also there. Any non-default instances can just be manually added.