I tried that once: A f_destruction about 200 times more powerful than the original w/4 stars. I made it so it couldn't be used in multiplayer, but it made SP too easy so I scrapped it. Never submitted it anywhere anyways, but it was interesting to test my cog skills. It was rather amusing, though, to play a level w/ all 7 dark jedi, and use it and see them all blasted away to the edges of the room and die.
But now I make new, real f_powers.
Back to the subject of having them used on servers: How about the servers have their own set of cogs, and use those instead? Might be a little editing of the engine, but I'm sure it could be done. Just not using any of the cogs it already had.
That won't stop players from making them with different file names and shortcut keys, but it would be a start.
I need a new sig...