Leaving aside all the legal arguments (not really the place to argue for/against), I am curious why you would want to do it?

Changing the IMEI can, in some cases cause the device to be blocked by some over-eager networks which use the EIR (Equipment Identity Register) function in network equipment to stop stolen mobile devices being used.

I can't tell you how to change the IMEI, but I would suggest you not to do it, unless you have a really good reason to do it.

Hope that helps.