I believe I know the answer to this, and it's "no"
We have a subset of hosts that are more critical than others, and I'm looking for a way to make them stand out more if they go down.
I could put a suffix on the hostname to make them more obvious. But is there any way to change the notification to anything other than "PING Critical - Packet loss = 100%" for these servers?
This is on a Core system, with all configs done manually.
I want to say "Absolutely", which is mostly true. You can definitely change the output through the use of a very simple wrapper script to call the plugin store the exitcode, return the output you want, and exit just as the called plugin did. The reason I cannot say absolutely, is if you are referring to making it stand out more in the nagios interface, in this case it would be quite a bit more tricky unless you are comfortable with C and recompiling nagios. You might want to look into Business Process Intelligence(BPI) as a possible interface that would fit you better.
Nagios-Plugins maintainer exclusively, unless you have other C language bugs with open-source nagios projects, then I am happy to help! Please pm or use other communication to alert me to issues as I no longer track the forum.