Jennifer. Think of someone who keeps order in the Wild West.
Last 4 letters are a word meaning "improvising on a theme".
I'm stuck with
18. He is chosen to serve but at the start very earnest novices somehow remain. (9)
93. Finding composer, Charlie, at the final concert. (7)
68. Marian loses the right to stop you in the road. (7)
I think they must be easy because no one else has asked for help. But they're not easy to me. Any help please