But the boarding passes won't have the same sequence numbers. The HTML hack just changes the displayed number at the bottom of the page.. the encoded barcode is still the same and would still refer to person #100 or whatever.

On most airlines it is pretty easy to forge boarding passes, but that doesn't mean it is worth the risk.. just ask the guy who created an online boarding pass generator for NWA and had his computer confiscated and is being charged by the govt...