This topic is of particular interest to me as an astrophotographer. The film I use only comes in 36 exposure rolls and these might take 3 or 4 months to shoot given the number of available clear and moon free nights. In the meantime I cannot obtain the feedback needed to adjust exposure times and settings for a given subject. A 100 foot roll would probably take the rest of my life to shoot. It seems to me the best solution is to simply shoot 10 or so pictures and open the camera in a dark room, cut the film and remove the cartridge. Then attach a reloadable cartridge to the exposed film end, close the camera and simply wind up the exposed frames as usual. I have done this before when a roll was accidentally broken while rewinding. It is no big deal and takes only a few minutes. The only downside is that dividing a long roll into several parts will increase the processing costs since each part has to be processed separately.
Astrojmn