This patch prevents Yoshi from eating a P-Switch in the "pressed" state, after which you could spit it with Yoshi and get a new P-Switch (and sometimes this also makes a fish spawn if it's spit at the right time).
(the gifs show before and after the patch is applied)
Yet another item for the "surprised this patch didn't exist already" pile. Simple and effective, and prevents setup-breaking switch duplication and weird fish/Podoboo spawning.
The code could be marginally optimized by hijacking $01AB0C instead of $01A202 so that the "inedible" flag only gets set once when the switch is pressed (which could also turn the "P-switch remains smushed before disappearing" time into a define for user convenience), but this is a nitpick of the most minor degree.
Tested with Asar 1.71, Lunar Magic 3.11, SA-1 1.32, Snes9x 1.59.2.