I think it will be a closed box with warranty voiding if you hacked it. Its a cool project to undertake having watched a video or two where someone programmed one themselves.
I never paid great attention at college but its a nice skill to have to be able to reprogram custom gauges or design something similar to the zx digital gauge.
The aftermarket however may be able to offer up something in conjunction with Nissan. Nissan may take issue with it. Depends
I think this is an interesting idea for the suggestion box. Z31 look dash as an option or via aftermarket.
@DAN_PASSE