I would think so if they are based on ARM (I'm guessing you've
checked) and you can trace the JTAG connections on the circuit board
(if that particular uC has them).
It must be possible - how on earth would they get a bootloader running
I haven't actually got an NXT to check but: check the chip it's based
on. If it's generic (philips, atmel, etc) lookup the datasheet and get
a pinout. If it's Lego branded, good luck - you'll need it!
Also, look for connectors, test points, etc on the board.
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