Brian Blair :
It will not void the warranty if you use ccc to overclock. Besides even if it did void the warranty, All you would have to do is not be dumb enough to tell them you overclocked it. Besides there is no way they can know you overclocked it. Unless you flash it with a different clock speed. But other than that they will never know. But if it is a 270 nonX model I would not go over 1050mhz, And I would not overclock the V-Ram at all! The 270's are already overclocked on the V-Ram from the 7870 and the 270 non X models have no V-Ram heatsinks. So overclocking the V-Ram is just going to ruin your card very quickly. Stupid bit miners can get away with it longer since they do not see artifacts as quickly. But it eventually happens to them too after it gets so bad. And then once the solder in the V-Ram chips melt more they will get red hot almost as soon as you turn on your PC causing blue screens. So never OC V-Ram without heatsinks.
I would advise against using CCC to overclock. You don't get much functions out of CCC. The preferable software that everyone uses is MSI Afterburner because it comes with RiverTuner and whole lot of functions generally not available even to other ones like Trixx.
MSI Afterburner allows extra options to extend overclocking ability, this means it allows you to push your card beyond the set limit which gives you more free performance. My R9 270 is able to achieve an additional 120mhz on the core resulting in 1190mhz, more than 25% than the stated overclock of 1050mhz on the chip. It also has OSD which allows the user during gameplay to view the current FPS, GPU temp/usage, VRAM, CPU, system ram, etc...
CCC is for basic amateurs who doesn't have a clue how to overclock so you can set the sliders all the way up and hence you limited your card's potential.
And no, if you do overclock beyond the stated OC limit, the manufacturers can actually detect the past settings your chip has been running in. They have a method of extracting back log usage that users can't. Hence when you do have issues, they can refute your warranty and its up to them if they want to send you a new card. That is why people who do overclock use benchmarking softwares like Unigine to stress their gpu to know the limits and not push too far.