Yes, good trick. But I didn't find in local hobby store the white enamel, there is only the acrylic paint. And I don't know if it possible to lay enamel over the acrylic and if it will be durable enough..That's why I want to go using airbrush. The airbrush allow to paint carefully covering the surface, as if falling from the top to down. And not to crawl through the stencil. The other one thing I want to say is that stencils a very good adhesive first time using. So If I'll be lucky to put it right way initially it will be no overspray totally, I'm sure. When you detach the stencil it going stretch and very difficult to use again without gaps. These are my observations when painting black stripes. So if I'll apply the stencil perfectly, I'll use just the brush easily.
The good thing is that trooperbay supply the double stencils in one set ($20), so if you spoil one sticker, you have the second one trial.