There is a template named Juniper MX204. This template has several linked templates, including one named ICMP Ping.

There is a template named SNMP reachability, and it has template ICMP Ping as dependency.

When trying to add template SNMP reachability to a given host, a message Cannot update host is presented, although template Juniper MX204 is already in use for this host, which has ICMP Ping template linked to it.{}{}

It should be possible to add template SNMP reachability to the host since ** Juniper MX204 template is in use and it has linked  *  *ICMP Ping template, and, somehow, host will have linked to it all the needed depedencies.{}