Being intensive or extensive property is not related to changing of system properties like concentrations. It is related to scalability of systems.
If you change the system scale, like doubling or halving it, and if the property remains the same, like temperature, density, composition, equilibrium EMF, it is the intensive property.
If you change the system scale and the property changes proportionally to the scaling, it is the extensive property, like mass, volume, energy.
If you change the system scale and the property changes, but not proportionally to the scaling, it is neither extensive neither intensive property. Like the object surface, galvanic resistance or the non-standard non-equilibrium EMF, where level of the electrode polarization can be scale dependent.