Just like the topic says, on a Cisco device...
I'm pretty sure the only way to change a password via SNMP is to use SNMP writes to TFTP new commands into the running config, and NCM doesn't support configuration transfers via the SNMP/TFTP combination. You could do this with any tool that allows you to do arbitrary SNMP writes, however (assuming the device allows SNMP writes, of course).
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