Keep your correspondence from looking like a computer-generated mass mailing. Keep it concise. One page is enough. Voice your concern in a civil manner. Nasty rants and raves are quickly dismissed.
Networks value demographic info.
So include your age, occupation, number of children, etc. If your passion knows no bounds, consider writing your local affiliate and the show's sponsors as well. You might want to mention something about the sudden move from Wednesday nights to Friday nights. People between 18 and 49 are going out, not sitting down for a night of television. That night is not our audience, and I'd love to be back where we were.