[SNMP4J] USM table

[Ramsey Hage]

Hello,
 
I have a management station that needs to add/modify/delete user
information from the USM table.
I do not use the engineID of the agents that I am monitoring.
 
I have used following to add users to the USM table:
snmp.getUSM().addUser( securityName,
                                      new UsmUser( securityName,
                                               authenticationProtocol,
                                               authenticationPassphrase,
                                               privacyProtocol,
                                               privacyPassphrase));

I would like to add another user to the table, with same securityName
but with a different authenticationPassphrase.
Is this possible (without using engineID)?  I tried calling the method
twice, but seems like it overwrites first entry...
 
If it is possible, how would I modify or delete the correct instance
(once the two entries are inserted properly)?