General Customized services extend to icmp
You can define customized services, for example tcp/udp port from 1:65535 to 4444. Also you can define custom icmp services, but it's not possible choice options out of RFCs. If you want define a ICMP service of type 1 (in RFC type 1 and 2 are unassigned), simply, you can not do it. It's not sense you can define your own service, but a custom icmp service does not be. By definition it is a "custom" not "standard" service.