Assumindo que suas regras anteriores eram assim:
nat on egress from 192.168.1.0/24 -> (egress)
no nat on egress proto udp from 192.168.1.10 port 4672 to any
um exemplo de fazer isso com as novas regras seria
match out on egress proto udp from 192.168.1.10 port 4672 tag NONAT
match out on egress from 192.168.1.0/24 !tagged NONAT nat-to (egress)