Even in the simplest MIDI system, there is often a need to switch between one MIDI source and another. For example, when editing, the input to the computer often needs to be taken from the output of the instrument in question, while the multi‑instrumentalist might need to switch between a master keyboard, a MIDI guitar and a set of MIDI drum pads. To use a programmable MIDI patchbay just for this purpose would be overkill, and if you can solder, it's far more effective to make your own hardware switcher.
The diagram in Figure 1 [sadly this is unavailable] shows a very basic, two‑in, one‑out MIDI switch box based around a two‑pole, two‑way toggle switch. However, multiple inputs can be accommodated just as easily by using a rotary, two‑pole wafer switch. Wafer switches are available with various numbers of positions; I use a four‑position switch in my own studio to give me four possible MIDI Ins. Such switches are readily available from electronics supply stores/websites.