Afaik there's currently no way to use the internal highlight feature to check the user's address. You're allowed to use custom identifiers just like you may use internal identifiers (like $me). But inside their scope, neither $fulladdress nor $address nor $site are filled with a value (at least one would be required for you), not even $nick.
If for example you would put this highlight:
$customhighlight( $!nick - $!address - $!site - $!me - $!1- )
and add this alias:
alias customhighlight {
timer -m 1 1 echo -s $!!1-: $1- target: $target nick: $nick address: $address site: $site
timer -m 1 2 echo -s chan: $chan cid: $cid network: $network wid: $wid
}
Some identifiers would be filled - but not the ones you'd need. (Note that without timer no echo will display at all.)
To have at least hostmask-related identifiers filled may be worth a feature suggestion.For the moment, I suggest to try the "nick colors" feature which allows you to highlight the nickname matching a certain mask in both the channel/query and the nicklist (but without any beep/flash etc options).
The other option would be to script your own custom highlight with "on text" and "on action" events (where $address etc are filled), replacing the default text display - like in a "theme"-script. The big downside is that it would most likely interfere with the theme you may actually use.