Just for the heck of it I tested the current draw of my A2 a couple weeks ago. It was 1.500 amps from fresh Battery Station 123 cells.
If you put the resistor in line with the rechargeable cells in the body, a couple things to think about; 1.5 amps is a lot of current, the resistor is going to get "warm" and you will be dropping the voltage to the LVR and lamp as well as to the LEDs. A bunch of resistors in parallel should be able to handle the load if you can't find just the right value in a high wattage resistor. But any extra capacity you would get from the higher voltage of the Li-ion cells will be dissipated in the resistor. This may not be an issue since the cells are cheap to recharge, but you'd get longer runtime by just adding the extra resistance to the LED circuit.
One issue that may come up though, will the existing resistance in the switch be sufficient to keep the LVR from powering the lamp in low mode given the 8.4 volts of the li-ion cells vs the 6 volts the light is designed for. If not, you would need the resistor in the body, or you'll have to increase the resistance in the switch too. Remember that the switch resistance is no longer in the circuit when the LVR/lamp is on, only the SMD resistors on the LED ring are protecting the LEDs at that point.
Hope your experiment turns out well.