Really is very difficult, iOS system is the most stable and strong OS on the world. But for any versiones, hackers on the world have gotten breaks the iOS security with jailbreak.
When the iOS security is hacked, may be is possible, but nowadays, is imposible do the jailbreak.
The only way to achieve clean an IMEI is when the network provider to approve IMEI cleaning. Any times there are private server to clean IMEIS.