Nah, I don't think Motorola's gonna do your upgrade kit. Its that private company Cellphonerepairshop based in Glendale that will do it. This will likely void your warranty but many of us are probably nearing a year on our devices anyway although Maxx was released more recently so a buyer could think he is getting some warranty although I think selling it may also void the warranty.
I'm not saying I could necessarilly do this especially to a friend, but if someone else did do it, I wouldn't be morally outraged or anything especially in a world of electronics where people do all kinds of mods to their stuff and pirate all kinds of things, at least this one with genuine parts and nobody may ever know.
Btw, I probably think you could change the device to indicate its a Maxx through root and SQL editor.