Ah, you think someone would do this to brick a device they don't own in the field?
Then I would make the method accessible, but behind some kind of authentication method. User mails you and asks for the way to install it, once you've verified it's really them you provide the unique backdoor to that machine. Might be one way to approach it.
You can burn a unique serial number or whatever directly into the IMX6, there's a eFuse/OTP driver that lets you access it from the filesystem.
Then I would make the method accessible, but behind some kind of authentication method. User mails you and asks for the way to install it, once you've verified it's really them you provide the unique backdoor to that machine. Might be one way to approach it.
You can burn a unique serial number or whatever directly into the IMX6, there's a eFuse/OTP driver that lets you access it from the filesystem.