As long as you are simply applying bullets to Normal, and maintaining Normal as your style; and as long as you wish to maintain 18 pts after in your Normal style, I don't know of a solution. It is easy enough to create a new bullet style with 0 pts after, but this you would have to apply as a separate style. Have you considered creating such as style and making a shortcut button on the Quick Access Toolbar?

Thanks for your help.