Once I needed to perform snmpwalk with a non-standard SNMP port, since the devices that were polled were behind the same router, so the ports were forwarded to them.
It’s simple, when executing snmpwalk, the port is specified after the IP address separated by a colon, here is an example:
snmpwalk -v2c -c ixnfo.com 192.168.5.5:555
See also my other articles about SNMP MIBs and OIDs