Thanks! Now that I know what it's called, it's much easier to find information.
I didn't realize you needed a different foot for monopods. The manual says you should not switch foots yourself; it should be done at a Canon service center.
I'm not planning to use the monopod foot, but what if I want to use a third-party foot? RRS, say. Can I do it myself? I always have before, but apparently this lens is different.