NEW YORK — Reworking old themes is always a challenge, particularly when an entire collection’s identity revolves around a single focal point. Case in point: M Missoni, in which the designers have to keep their signature knits fresh-looking and of-the-moment season after season. This fall, they did it with panache, pairing their sweaters with leather pants or a corduroy jacket and even a sweet little tweed skirt. Meanwhile Gianfranco Ferre Studio, right in sync with the season’s tuxedo craze, reworked the classic evening suit into a ruffle-front black tulle wrap blouse worn with long, full satin pants or a long silk jacket that ties at the waist. And of course, there were great looks for day such as the tan cashgora coat, orange leather miniskirt, fine knits and slim pants.