https://sourceforge.net/p/net-snmp/mailman/message/35520237/

Due to some internal logic in net-snmp this can not be done so easy.

A first test shows that when enabling a hypen in the regex net-snmp will convert the username from ascii-string to hex notation:

0x736e6d702d6d6f6e = snmp-mon

snmp {
    v3 {
         engineid 0xaffebeef
         group default {
             view default
         }
+       user 0x736e6d702d6d6f6e {
+       }
-       user snmp-mon {
-       }
    }
}