Check under this code's tab "Shadowraze", you'll find something like CONFIGURABLE :
And when you go through every line you'll eventually notice this :
JASS:
// range of "Shadowraze (Z)"
private function GetRangeZ takes integer level returns real
return 200.0
endfunction
// range of "Shadowraze (X)"
private function GetRangeX takes integer level returns real
return 450.0
endfunction
// range of "Shadowraze (C)"
private function GetRangeC takes integer level returns real
return 700.0
endfunction
All you have to do is modify those values...Also you remove both spells with hotkeys "C" and "X" and just use "Z" with your custom range.
I am not professional in JASS but I guess you can replace the value by a custom variable.