It is best to short out each capacitor to remove the charge before attempting any modification or measurements. To discharge, simply use a resistor or close the loop. Electrons like to move from high PE to low PE, and discharge is instant. Charging takes a few second. Devices that obey Ohm's Law are linear devices.
Diodes are non-linear.
A perfect diode actually funcations like a switch - turning on and off. The switching action of diodes if of fundamental importance in electronics. This sensitivity to the polarity of a signal finds a multitiude of uses. Diodes allow a current to flow one way, preventing current from returning back. However, if enough electrons builds up, a avalaunch voltage may occur - when the electrons just breakthrough the dam holding all the water and flood backwards.