You CAN, but you're better off using Tamiya's own thinner for smoother finishes. Tamiya's paint dries pretty quickly as it is; rubbing alcohol will only make it dry faster and possibly before it hits the model, depending on the temperature and humidity.
If you're shooting gloss colors, try using lacquer thinner. Tamiya's paint is actually a lacquer/acrylic hybrid, and glossy colors go on much smoother when you thin them with lacquer n.