Have a few effects that don't fit on my pedal-board, so am wondering if I could build a small footswitch to control them from my board, and if there is a more nuanced method then just using a multi pin cable?
I don't know a lot about it (though hopefully one of the many here that do will chime in), but if you use relay switching then you can use a momentary SPST, which means you could use a simple guitar cable-type connector for it and just have the switch itself in a tiny box on your board.
you can also do this with most 'non-true bypass' pedals, a spst momentary wired in parallel to the actual spst momentary switch in the pedal, and run remotely with a cable to your pedalboard or wherever... hitting the remote switch or stomping on the actual pedal both work to flip the flipflop circuit on to off...
you could do a 1/8" mono jack in the pedals and another for the switchbox then a length of 2 conductor cable/ speaker wire.