HaloMods "Classic" Read-only Archive

If it's in the XBE, where is it cached? I already searched the original XBE. But either way, wouldn't moddifying the XBE not allow me to play on system link(with other people that have the original XBE)

What file would I edit though?

Would I edit the maps?
If so, would I directly edit the .map files, or would I have to edit the cached maps?

I've seen it done, but I cannot find any information on it.
The text I'm talking about are things like "You killed...", "Double Kill", etc etc.
I've searched through these forums and others too, but no luck.

Does anyone have any information on this?