I have replaced the headphone resistors with 10K ohm to gain equal AF level between the speaker and my head-set.
A 220 ohm/1W resistor has been inserted in the supply to the rear fan to reduce speed and noise. I am looking for a circuit to control both fans thermostatically! I have now disconnected the rear fan completely, to no ill effect, although I would think twice if living in a tropical climate - Caveat emptor, let the buyer beware!
68K ohm has been inserted before the audio chip to improve the AF level control.
As mentioned above, I have also replaced the PL socket for 144 with an N-socket.
While replacing a broken On/Off switch (For the third time in 6 years! (Shame on Yaesu)), I created yet another useful (for me at least) mod. Often, while contesting or DX'ing with headphones on, I have guests in the schack who want to listen in, instead of fooling around with external splitters etc. I just soldered a 47Ohm resistor over the headphone switch so that instead of muting the speaker completely, it now just reduces output.