Why did not you ask the Cat?
/ip firewall layer7-protocol remove [find where name=123321 or name=654654]
:global jobID *0
:global EventHandler do={
/log info "On $1 is added a new item $2"
:return 0
}
:set jobID [:execute ":global EventHandler; /ip firewall layer7-protocol print follow-only where [\$EventHandler \"layer7-protocol\" \$name]"]
:delay 2s
/ip firewall layer7-protocol add name=123321
:delay 2s
/log info "kill the EventHandler"
/system script job remove [find where .id=$jobID]
/ip firewall layer7-protocol add name=654654
One hint:
Is possible to create a global array with event handler names and relatve job IDs