Sure, when we alter the body, alter the sliding mechanism, alter the keymat, alter the PCB accordingly, then basically everything is possible. What's NOT possible: that we alter any of the above, except for PCB but that's determined by the other parts.
And I still fail to see how software is related, we don't have T1000 metal that can change the mechanical properties by a command from software side ;-)
The 5-row kbd shown is a prototype for the GTA04 and not intended to get used for Neo900, except for the dome switch springs.

Of course you're free to casemod your Neo900 all the way you like, and connecting whatever kbd you like is no problem, neither hw side nor sw.