If you mean can you cut privets in winter, whilst they,re dormant ?, then the answer is yes you can, if you want to cut them to reduce their height, you can cut them back as far as you like, and they will regrow in spring, cut them a few inches lower than you want the eventual height, so that when you trim them, you don,t catch on thicker wood.

But if you also want to make them narrower do one side one year and the other side the next.