|I have a spiral cut juniper thats about 7|
|Topping a juniper will certainly shorten it, but the plant will likely produce multiple leaders (upright growth) and you'll eventually end up with a pom-pom at the top of the stem. I'd be more inclined to find another home the the spiral juniper and select a different plant for the site. There are smaller versions of the plant, or you could choose a slow growing conifer that won't need constant maintenance to control the size.
Best wishes with your landscape.