In the settings for SNMP you have the snmpd.conf file editor. The line
rocommunity public
is the default but the community string can be changed to what ever you want. (this causes the plugin to uninstall on the next boot.)
Security best practices are to change the read only community string to something else like changing a default password.
The snmp.plg is doing the following to verify if the plugin was installed.
results=$(snmpwalk -v 2c localhost -c public hrFSMountPoint 2>&1) || printf "snmpwalk failure"
snmpwalk is connecting to the snmpd service and using public and the connection string.
If you change the rocommunity string snmpwalk command fails to connect and uninstalls the plugin on the next boot.
I would guess that to fix the issue with changing the rocommunity string the plugin should read /etc/snmp/snmpd.conf and get the string for the rocommuntiy line as a variable then use that in place of public for the script.