Hi Vapetech,
As far as modding the 470pot you have there you could parallel another 470 to the two legs of the pot to give you a final high resistance of 235...... but when you are adjusting the pot you will notice that the response curve is different than it should be..... In my opinion you should just get the correct pot. I have tried the above and it did work but the output was noticeably wrong so I pulled it out and waited a couple days for the correct parts to arrive. This is the one I have been using for a few years worth of Raptor builds : 3352W-201LF from Bourns, Its is much more space friendly than the volume knob you have listed, and can be turned without having a tool.
None of those chargers you have listed will work unless you are going to build a separate circuit to parallel the batteries in the mod just for charging. The Raptor mods use the two+ batteries in series, so you will want a balance charger or to remove the batteries from the mod for charging on a desk charger.... This is also and option if you want an onboard charger for the two batteries in the mod :
http://www.varitube.com/YiHi-9V-Balancing-Charger-Board_p_179.html but I have never used it so I cant say how well it does or does not function, or how safe it may or may not be.
Reverse protection IS not hard to achieve, for fool proof reverse you just need a small mosfet. This is the one I have used for quite some time : IPD042P03L3 G from Infineon Technologies. It is very small and works flawless. I have destroyed 3 different mods by inserting batteries in reverse, until I began wiring this simple little mosfet into my builds....... Never had another issue after that.