Undervolting will not break warranty; you're not replacing anything and its just a down volt of the CPU to use less current.
And for those who are wanting to try UV'ing...
If correctly done, the chain reaction for UV'ing thus consume less power, saving battery life and reducing heat dramatically. Coupled with a MX-2/AS5 application onto both the CPU core + GPU will yield cooler results.
If by Undervolting you get a BSOD, then increase the voltage up by one step higher in RMClock. The BSOD happens if you undervolt its voltage too low. The BSOD is harmless. I've experienced it many times before. If it BSODed, RMclock will reset its to its stock CPU voltage automatically after the reboot. Just remember to use the next higher voltage that you last used prior that caused a BSOD to happen.
Remember to do a half an hour stress test using Orthos, Prime95 or IntelBurn after UV'ing to check its stability. Likewise increase the voltage one step higher if you noted a BSOD during the stressing.
CPUGenie isn't free, which is what I do not like about. RMClock is fine. Make sure you go to Advanced CPU Settings section and under the CPU type selection, select "Mobile" then restart. It will help to read the voltages correctly.
Yeah, I do not like the sound of that GTX 260M heating up to 99*C.

if you're hands on, you may want to try accessing its cores. (remove the heat sink first, then the copper casing) and apply thermal paste on it. Yes, thermal paste can be applied to GPUs as well.
I will gladly assist if you need more help cooling down your GTX 260M. There are other strategies like volt modding to run cooler using Nibitor (It's the "RMclock" for GPUs) which I have tried but I wouldn't really recommend it as it's quite risky as it requires flashing the vBIOS and if you don't know or unsure what you're doing.