1.you can use "alter system set instance_name" to change the value of instance name.
2. you need to do the following to activate the standby database (NOTE:-this is only for activating the standby database and not for switchover of database)
1. startup nomount
2. alter database mount standby database.
3. alter database activate standby database.
4. alter database open.
only "alter system set instance_name='TEST' scope=spfile" will work since the parameter INSTANCE_NAME is static. After restarting the database/instance the statement "show parameter instance_name" will show the new instance name.
But when selecting the view V$INSTANCE the value of the column INSTANCE_NAME has still the old value. Any idea why this value remains unchanged in the view V$INSTANCE?