Yes, it's probably a bad idea. Why do you want another rooster?
Bringing in any new bird stresses the flock. If the new rooster is sexually mature, he and the current rooster are going to have to figure out who is boss, and that involves sparring at the least, hard-core fighting at the worst. He'll also have to convenience the hens he's dominant to them and allow them to mate with him.
If you free range, things could go better, but if your birds are cooped, unless they have tons and tons of space--I'm talking over 20 square feet each--I would't do it. There would have to be a ton of gain from the new rooster to disrupt the flock that much, and if the new rooster was worth all that, he would be replacing the current rooster.