I originally thought that this was not possible but after reading some things I'm wondering if there is a way to do this.

I have 2 devices that pass through a small external circuit of resistors that selects the voltage for the device (for a power supply) . There is a switch that selects preset resistor loads and also a potentiometer. Both devices are identical and require the same resistance settings. Currently I have 1 circuits for each device. Is it possible to put a diode (or multiple) somewhere on each device to allow for the current not to flow from one device to the other?

 

Possibly. You really need to post some kind of a schematic to give us a decent idea of what you are dealing with.