You should be fine applying a lacquer top coat over the primer, as the primer is also lacquer based.
However, the question remains. How are you applying the colour coat?
If you're applying it directly from the spray can there's no way to thin it.
If you're decanting the paint to apply using an airbrush, you shouldn't need to thin it as it should be thin enough to airbrush and you can control the amount of paint delivered by the airbrush.