"I am looking at a cb that has a "modulation kit" installed -- If this were used with a power mic, would that over-power the rig?"
Most of those "modulation kits" are pure B.S. and will cause over modulation even if done correctly. Using that 'kit' with a power mic is just more of the same.
Having more than 100% modulation is a waste of effort because it causes distortion. Using a power mic can do the same thing if it's run at too high of a setting. Add the two together and what do you think you get?
Will doing either raise the output power of a 'stock' radio? Probably, but that increase in power isn't going to be noticeable. What you will notice is a difference in how the user 'sounds', and that's usually not 'better' by any stretch of the imagination. For an increase in power to be effective it means you have to at least double the output power. Unless you want to do a lot of modifying, a stock radio just isn't capable of producing that doubled power, the manufacturer isn't 'giving' you something for nothing. Those just looking for 'bigger numbers' don't understand those 'numbers' to start with so think they've really done something useful/beneficial and it doesn't mean a thing.
You can 'push' almost anything to some extent, but you have to know when to quit before you mess things up. Most of the modified radios you will hear are totally messed up...
- 'Doc