[deleted] The only real supported method would be airplane mode with wifi on.
To be honest, I've never researched this in depth myself, so I don't know much about the topic, but it's my understanding that it doesn't really work. There are other identifiers that are involved in communicating with a cellular network, and some apps that claim to change IMEI just change a value in Settings, but the real IMEI is still used.
Not to mention that the methods that I know of require rooting, so they're unsupported.