How did I flip some mirrors around in the dark at 3 AM and change the focal length of a 24 inch Boller and Chivens?
What you did was to switch in a Coudé mirror, which sends the light down the equatorial mount as you described, to other instruments (besides the original focal point of the secondary mirror)
There are several designs to a Coudé path. The simplest uses a flat mirror and then places a second camera at the re-positioned focal plane, or re-images that focal plane using relay lenses.

Other designs can use a convex mirror as the first Coudé mirror to extend the focal length and send the light down into a &quot;Coudé room&quot; where other instruments are located.