A: You can easily destroy it and re-setup everything on the fly.
$ORACLE_HOME/bin/emca -deconfig dbcontrol db -repos drop
You will be prompted to give SID, listener port number, SYS/SYSMAN password and that is it.
$ORACLE_HOME/bin/emca -config dbcontrol db -repos create
you need SID, listener port number, SYS/DBSNMP/SYSMAN password. Another
2 optional thing are Email address for notifications and Outgoing Mail (SMTP) server.
Quicker than you think, right?
Note: there is a trick when play with 10gR1 instead of 10gR2