how to change hostname or domain for oracle application server

http://download.oracle.com/docs/cd/B14099_19/core.1012/b13995/host.htm#CIHJIBAG
Follow these steps for each middle-tier instance on your host. Be sure to complete the steps entirely for one middle-tier instance before you move on to the next.

1. Log in to the host as the user that installed the middle-tier instance.
   
2. Make sure your ORACLE_HOME environment variable is set to the middle-tier Oracle home. Do not use a trailing slash (UNIX) or backslash (Windows) when specifying the variable.
   
3. On UNIX systems, set the LD_LIBRARY_PATH, LD_LIBRARY_PATH_64, LIB_PATH, or SHLIB_PATH environment variables to the proper values. The actual environment variables and values that you must set depend on the type of your UNIX operating system.
   
4. Run the following commands in the middle-tier Oracle home:
   
   • On UNIX systems:
     

     cd ORACLE_HOME/chgip/scripts
     ./chgiphost.sh -mid
     
     

   • On Windows systems:
     

     cd ORACLE_HOME\chgip\scripts
     cmd /c chgiphost.bat -mid 

     Verify the logs 

     What Changes Are Required to OAS when the Server IP Address or Machine Name is Changed [ID 569931.1]
      

     Goal

     What changes are required to OAS when the server IP Address is changed ?
     What changes are required to OAS when the server machine name Address is changed ?
     

     Solution

     If IP address has been changed, Administrator only needs to use the CHGIPHOST script. The script is located at \CHGIP. The simplest way to run it is:
     
     1. Stop the application server (i.e. stop the service, or issue [OAS home]\opmn\bin\opmnctl stopall).
     2. Open a Command Prompt window.
     Set ORACLE_HOME to the location of your OAS Home (e.g. D:\ORAHOME_1).
     3. Change into the directory [ORACLE_HOME]\CHGIP\SCRIPTS.
     4. Execute the command CHGIPHOST.BAT -mid    (for default deployment, other deployments may require other options).
     5. Respond to the prompts. "Source" means currently configured values, and "destination" means new values. Host names should be entered in fully qualified (FQDN) form (e.g. myhost.domain.com). If you are not changing a value, enter the same value for both source and destination.
     
     Administrator would enter the same FQDN for both source and destination, but would enter different IP addresses (old/new).  Please refer to the OAS Administrator Guide for additional information (avail on http://otn.oracle.com). It has very in-depth information about the different scenarios in which this tool is used and how to apply it to different deployment architectures.
     If host name or domain have also changed, then there are several other areas (outside OAS) that need adjustment as well.