I bought a 99 z28 and there was spark plugs 2 steps colder for the zex nitrous system installed, I don't plan on using the nitrous for a long time, r there any benefits to using 2 steps colder spark plug? Safe? More or less horsepower?

 

There is no benefit to running cold plugs on a stock motor. If you don't plan on spraying just get some stock heat range plugs.

 

The plugs are only a few weeks old tho, just wanna know if I can leave them in safely or if it hurts anything

 

Yes you can run the colder plugs. The only risk is that they will be more prone to fouling in continuous low rpm operation. In theory, there is power to be made by running the coldest plug that will not foul if it permits more aggressive tuning parameters such as spark advance. The amount that can gained is minimal when it comes to computer controlled, fuel-injected engines.