you definitely need to remove JP36, or the resistor will have no effect.
the purpose of adding the capacitor is so that the modulation will not be attenuated by the resistor being there.
there is a DC voltage coming from the modulation transformer, through a rectifier diode, and going to the collectors of the driver and final transistors.
this DC voltage sets the deadkey level, and there is an AC component "riding on top of" this DC voltage, and that is your modulation.
when you add the resistor, you lower the DC voltage to the driver which in turn lowers your deadkey. however, that AC voltage (your modulation) has to also go through the resistor, which lowers it's level.
so, the capacitor gets added because a capacitor will pass AC but will block DC.
so now, the deadkey is lowered, but the modulation still passes without being lowered.
you can also lower your deadkey without affecting modulation by adding more rectifier diodes in series with the one coming out of the transformer.
hope this helps.
LC