Making specific notes silent

I am writing a piece for my Jazz Band and in the piece I have the trumpets clap. I put the clapping on the B line, where it usually is, and added the "x" note heads. However, during playback, I can hear them playing the notes, and I don't want this to happen. I'd mute the whole track, but later in the song they play notes which I want to hear. How do I set the notes to be silent?