Its getting harder and harder to break the rules in Mexico...as I've broken them all. I've temporarily imported three bikes in the last five years and the border officials have become very anal about reading the VIN number on the way out. If they don't believe this is the same bike, all they will do is not cancel the exit and you will forfeit your deposit...about $400. You can still leave the country as they will not throw you in Jail. Besides losing your money...the only other consequence is you will not be able to import another vehicle on the same passport number. This can be solved by getting a new passport as the paperwork follows your passport number and not your name or VIN number.
I don't think you can get a new VIN number on your bike. Good Luck!