Would turbine blade twist change if all conditions except the density of the fluid remained the same?
A classic comparison would be boat props vs aircraft at various RPM.  A higher density (viscosity) fluid would put more stress on the blade tips, hence shorter and more robustly built blades.  The amount of twist would depend on loading of props and would include chord length.  A tapered prop may have a different twist from an untapered or reverse tapered.  Diameter and RPM are also factors in loading.  And, as in aircraft, twist would also play a role in cruise efficiency or acceleration from standing still.  

So there is no one rule about this going from one fluid to another (rare application).
Variations of design and performance in one fluid are much more common.