Yeah, even though the other side couldn't hear it, I made an awesome Wrath of Khan taunt mod last year, that amused me to no end in SFC2: EAW.
I'm sorry to hear that no one has been able to do so in SFC3, surely there must be a way I hope?
As far as customized Taunts shared over internet games, I believe Wing Commander Armada, was one of the first games to ever do this.
If it was done back in the mid-nineties, I would imagine it would be even easier to do these days.
If I ever get the time this year, I would like to donate my humble programming skills to help make a music/taunt mod based on music and threats made from the DS9 and TNG series and related movies, that may become a must have add-on for SFC3 players.
Is anyone already in the process of doing this yet??