Ha ha ha... Wow "You can and will get banned" OMG i'm on the floor...
1. "thermal sensors" if you will, are built into CPU and GPU Not the case.... What in the world would be the point in that? That would void the point in even having them in the first place.
2. "IF" (and there NOT) Microsoft was watching for heat changes, who in there right mind would open there 360 while it is running???? Just absurd. Not to mention there are to many variables for them to use temperature to detect such things.
3. Have any of you actually opened a 360??? NO!! I doubt it. There is absolutely nothing connecting the case to any special gismo to detect if it has been open or not. It's like in the days that people thought there was a chip breaker in there lol.
4. The only way your going to get RROD (general hard ware failure) from opening your 360 is if start playing 5 finger fillet with the chip set, spill something, have a static discharge,knock something loose, rub it across your cat... And none of these are a sure way to get RROD.
In conclusion, No you will not get banned from opening your case, but if you rely on the warranty don't open it. Microsoft does not give a rat's hat about temperature variation. They do not install "Thermal sensors" to the case... That one befuddles me to why you would think that. Some times I wonder how all of these gamers don't know a flying fig about there console.... Just freaking puzzles me.