CEL For if condition
 

The fluid is magnetic depended and it should be specified separately.
another case is the non Newtonian is separated by Newtonian.

I am using if(inside@piston == 1,a, 0.11 [kg m^-1 s^-1]) condition to differentiate Newtonian and non Newtonian region in material properties.
I wanted to add another region to this if condition, could help me how to

Then you just add more if statements, of course.

But this method only works for very simple cases. You might want to consider the more general case where you model the magnetic field (at least its intensity) and make the material properties a function of the field.