Hi TDNY,
Yes it works the way you did it. Basically, if the service/application is a standard defined one using a non-standard port you can inherit the configuration of the standard service/application already defined in Junos using the "application-protocol" stanza and modify the parameters that are different.
If it is a totally new/non-standard application protocol that isn't defined in Junos you can simply use the "protocol stanza" and set it to tcp or udp ( depending on which it uses ) and set its destination port, this is as simple as it gets; but you can also tie down other parameters depending on your understanding of the protocol. This is how it should be ( you missed out the parentheses) :
application udeploy{
protocol tcp
destination-port 7918
}
or :
set applications application udeploy protocol tcp
set applications application udeploy destination-port 7918