Originally, "reset dhcp" commands worked by mangling the leases file. This is fragile and inconvenient.

DHCPD provides OMAPI, an API for managing its state, and omcmd/omshell client commands. The only problem is that it cannot limit access to it by source interface.
Apparently the only solution is to automatically insert iptables rules based on options.

I suggest this default configuration:

dhcp-server {
  omapi {
    port 7911
    allowed-interface lo
  }
}