I'm playing Linus and Lucy and when it changes after the intro and the repeated chords to a different feel and rhythm, there is a C.M. above that measure where it changes. What does this mean?
It means Common Meter. It's an old american marking that is quite unusual these days.
You sure it's not "N.C." ? I see that in several online sheet music versions of this song. Dolmetsch Online says that means
chord symbols, there may be a bar (or several of them) that has no chord symbol. In this case, the performer continues playing the same chord as indicated in the previous bar (or measure). N.C., meaning 'no chord', is used where no specific chord is to be used at that point in the music, although when the melodic material has a strong harmonic element the marking N.C. is probably inappropriate [entry prompted by Tammy Ford]