Your friend will either be getting a
Invalid disc. "DNAS Error (-402) A PS2 disc information error has occurred."
Invalid or corrupted disc authentication data. "DNAS Error (-403) A PS2 disc information error has occurred."
Meaning that DNA$ has detected his chip, which is what happens when trying to play an original store bought game online without disabling your modchip.
If he puts the chip into standby or switches it off when playing originals online then he will connect fine. There's no need to change console IDs the PS2 isn't banned. The only time you would need to chnge console ID is if you want to play games from a region other than your own ie: a game in a PAL region if you're in a NTSC region. Sony only ban consoles for gross misconduct or cheating.
Alternatively, he could make a backup of the original game, patch it with the correct DNA$ ID & not need to worry about disabling the chip as DNA$ won't detect the chip when using a patched backup.
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