Steps involved in moving WebSphere dmgr from one host (machine1) to another host (machine2) with the hostname change :

1) As a caution make please make a backup of the following so that it's easy to restore when something goes wrong,
a) Backup the configuration of all the profiles (DMGR) and (AppSrv) in machine1 that is involved in the cell .
(eg) basically run WAS_ROOT/bin/backupconfig.sh which will create WebSphereConfig_2007-11-16.zip
b) (Optional) Also do a filesystem backup of the directory if possible to avoid any surprises.

2) Install WebSphere ND in the new box and create a new Dmgr profile with machine2_dmgr_profile .

3) Extract the WebSphereConfig_2007-11-16.zip to <machine2_dmgr_profile_root>/config directory.
(eg) jar -xvf WebSphereConfig_2007-11-16.zip

4) if <machine2_dmr_profile_root>is different than <machine1_dmr_profile_root> than change USER_INSTALL_ROOT "value" in /config/cells/<cell>/nodes/<nodecellmanager>/variables.xml to point to the new dmgr profile location.
(eg) <entries xmi:id="VariableSubstitutionEntry_2" symbolicName="USER_INSTALL_ROOT" value="/usr/IBM/WebSphere/AppServer/profiles/Dmg
r02" description="The filesystem path to the user installaton directory."/>


5) Change the following properties in <machine2_dmr_profile_root>/bin/setupcmdLine.sh to point to the machine1 dmgr cell name and node name.

(eg) WAS_CELL=machine1Cell01
WAS_NODE=machine1CellManager01

6) Copy the custom keyfiles (*.jks) from <machine1_dmr_profile_root>/etc/ to <machine2_dmr_profile_root>/etc; or skip this step if dmgr is using the default keys.

7) Follow the instructions mentioned in http://www-1.ibm.com/support/docview.wss?rs=180&context=SSEQTP&q1=best+practices&uid=swg27007419&loc=en_US&cs=utf-8&lang=en from page 4-6 on section 2 and 2.1

8) check if syncs works for all the nodes and you were able to see all the configurations from the previous dmgr.