This idea just struck me as something a little fun, just for the interesting mash-ups people might come up with.
Firstly, you need to pick a Trek series.
Then replace as many of the characters as you want with others from any other sci-fi franchise (at least one of the original characters must be left though), but you can only use one character from each show/movie (so no replacing the entire TOS cast with that of Firefly, no matter how awesome that would be). Also you can't use characters from other Trek series/movies, the replacements must be from outside the known Trekverse.
For example:
TOS. Replacing Spock with Yoda, McCoy with the Tenth Doctor, Uhura with Delenn, and Chekov with River Tam.
Firstly, you need to pick a Trek series.
Then replace as many of the characters as you want with others from any other sci-fi franchise (at least one of the original characters must be left though), but you can only use one character from each show/movie (so no replacing the entire TOS cast with that of Firefly, no matter how awesome that would be). Also you can't use characters from other Trek series/movies, the replacements must be from outside the known Trekverse.
For example:
TOS. Replacing Spock with Yoda, McCoy with the Tenth Doctor, Uhura with Delenn, and Chekov with River Tam.