Aside from the mechanical difficulties, part of the problem with stopping down a Cassegrain variant or Maksutov is that the central mirror becomes a larger percentage of the aperture, causing diffraction problems in the same way as stopping down a regular lens causes diffraction limited resolution at smaller apertures.

Astronomers do make their own aperture masks to place in front of Cassegrain and Maksutov telescopes. They are typically off-center, and stop the 'scope down pretty far. An aperture mask with two, three, or four holes is often helpful in fine focusing for astrophotography. A single hole offset aperture mask can provide a helpful increase in practical (as opposed to theoretical) resolution for viewing bright objects like planets and the moon. I use one with a solar filter for viewing sunspots.

A single, offset circular aperture mask will also eliminate the doughnut shaped out-of-focus highlights that many find annoying. Maksutovs are normally already pretty slow, as are some Cassegrains, and there's typically not a lot of room to play with making a smaller aperture on one of these optics designed as a camera lens, but if you have a large enough aperture and can afford the loss of lens speed, a mask might work for you. It's very cheap to make one and try it.

Lee