Casio CZ/ VZ/ FZ - Pro Series

>I wonder if it's possible to somehow replace some cz101's sound chips
>with those of a CZ 5000 to get the additional waveforms and velocity?
>I know that sounds kind of silly, but I'd like to customize my CZ101
>to have the features of a cz5000 and keeping it small.

As far as I know (which I don't really but it's a good guess), the CZ-101 
and CZ-5000 use the same sound chips, the CZ-5000 just has twice as many for 
double polyphony.  It's the controlling electronics that are different.  
Modifying that would require you to put the guts of a CZ-5000 into the case 
of a 101.  I really doubt the results of that would be "small".