They can triangulate your position based on the cell phone towers but that will be just an area of about 25+ meters. Not anywhere as accurate as a GPS signal. Technically anyone can triangulate cell phone signals with the correct software that allows you access to tower information which I actually have in hand, its called TEMS from when I did some RF engineering work when T-mobile first rolled out its 3G network a few years back
.
Your going to have to do some really hot shit however to get them to even try and triangulate your position. The most likely scenario is them just contacting the carrier and shutting off service. Triangulating is better suited to prove that a specific person was at a specific place at this time and date.
About changing the IMEI, it is possible and actually some hackers steal IMEIs from legit cell phone carriers to clone black listed cell phones but this would only work for a few weeks at the most until the carrier figures it out. I forget the name of the OS that the hackers install but it acts like a trojan and is usually aimed at Android devices.