Whopper is right!
To answer the first part of your question, is yes you can ad another tune to your SS
If you look at my signature below I added the HP tune to my car as well. And picked up even more HP. But I have to agree with whopper you have a problem that needs to be looked at and corrected. I don't think that would have anything to do with a tuning issue.

 

No, cat is still involved. But I've been keeping my eye on the code_which has been a no show lately

I have to re visit this when it's back

My dp is from a Cobalt owner who backed out of a custom job, so I have it now. That goes into the Magna flow

Still learning about my car. Its a little different than the 86 Bronco..lol..

 

when you drive into a Chevy dealership, The first thing there going to not do is ask you if you have a tune, "Oh you do" we won't work on any car with a tune. BE GONE YOU TUNER INGRATE!! :) lol But if there is some work that may have to be done that will cause them to have to reflash your tuner "ECM" then you will have to go back to your tuner and have them reflash your tune again. But you need a new water pump or alternator there wont be any issues. example if you buy brand new 20" rims and tires and the car seems to be pulling to the right. The dealers going to say take it back to where you bought those tires they know all about this after market rim and tire, second part of your question is yes they will install it! That's what I did I bought GMTU tune on line from an aftermarket company they had no problem with that at all! Keep everything completely stock! and you wont have to worry!
Tim