Not by using the RF Gain control with the resistor you used in the swing mod. Sure way to burn up that RF Gain pot. They cannot handle that much current and fail. Newbees do this all of the time and wonder why the radio stops transmitting after a while.
There are two ways: one is to put a pot on the pre-driver, and the other is to make a regulated circuit to control the voltage. Did you understand my previous post concerning over-driving the final after doing a swing mod?
IIRC; isn't there a known way of using the panel buttons on the LX model to make the radio do variable power? I have a vague memory of that; not quite sure any more. I usually work on SSB radios and don't really mess with AM only radios any more . . .
