There are quite a few individual races for Star Trek but I don't think there is a "just Star Trek" mod that turns SE IV into the Trek Universe. There is the 'SciFi Crossover Mod' that tries to bring all the major ScFi universes together, though. There's a thread about it on this BB right now. And the Jraenar make pretty darn good Gorns without any modding, anyway.
Oddly, none of these mods include the Tholians, as far as I know. I hope someone does them one of these days. Their ships would be very cool looking.