Go help with IRCv3 - you're talking about capabilities, which are part of the v3 protocol.
The trick with capabilities is you need them to be reasonably standard. Which means the go to IRCv3 server should ship with them turned on, and the reference client should be capable of using them.
But it's not possible to get what you're asking without breaking the IRC protocol - it's not easily extended and the formatting rules are icky mIRC crap.