Replace switching diode with MOSFET for lower voltage drop in charge pump?
No, you will need a more complicated circuit hanging off the gate of the PMOS. The simple PMOS "diode" circuit, unlike a real diode, is able to conduct in both directions if it's on. What determines whether it is on is if the "cathode" voltage is positive relative to the gate terminal.

That's not a problem if what is on the cathode end is something like a resistor which can only develop a voltage drop if there is a power source connected to the "anode". But it's a problem if what is on your output end has its own energy supply like a charge pump since it can maintain that voltage that keeps the PMOS on in the absence of a supply on the "anode" end. It can push current back the other way.