In most of the corporates have Disater recovery or failover environments.
Practically,in Informatica 8.1 you can create only 1 domain per DB. For Disater Recovery, you may require to use same DB by informatica application in different server/ you will be using differnt db all together.
The very problem comes when you go for installation.
What we did..
for Stand by application, we installed it by pointing to dev db with same Domain name , node name, port as in live server.
after installation, we updated the repository so that it's pointing live informatica repository DB.
If you want to use the informatica application permanently by retiring the live server, then, you can update the hostname of 'PCSF%' and OPB_Reposit tables.
if you want to use it as stand by then update the hosts file with live server name and ip address of stand by server