I dont think it will hurt anything but you will only get one side of the music if you run it like that. Some songs play different instruments between left and right and also you will lose all audio if the music shift to one side. If your not running rears, some component systems let you power the mid speaker separate from the tweeter through the same crossover.
I dont know if you want to spend that much.
If you put an extra set of tweeters, the highs might be too rich and it will annoy the hell out of you.