The reaction wheels rotate the satellite only about the centre of mass.If the reaction wheels are not placed about the principal axes,Will the amount of torque produced be the same as when they are placed about the principal axes?
The torque will be the same - application of point torque to an object (in this case the point is the reaction wheel motor axis) results in the same torque exerted regardless of the point. But the moment of inertia won't be - because the layout of mass will differ. As the reaction wheels are not massles, they are a part of the system, and while mass won't change, its distribution - distances from center of mass - will differ. And as result, the cubesat will react differently than one with the RW axes through its center of mass; in particular with mass distributed broader (farther from center of mass) the same torque will result in lower angular acceleration.