Could a lamp plugged into an outlet be dimmed using a variable resistor

Lamp dimmers change the brightness of light bulbs by delaying the turn-on of the output till later on the AC cycle as shown below.

This scheme works pretty good for resistive loads like incandescent light bulbs. It does not work very well with the cheap transformers found in the AC transformer type wall warts. If the transformer ends up being able to pass the chopped waveform then there will be a some reduction in the output voltage for non-regulated output type wall warts.

Virtually all of the newer type of universal type AC to DC switcher type wall warts will not be too upset with being fed a chopped type of AC input waveform. That said though most of these switcher types are designed with a regulator inside the wall wart that produces an certain output voltage. The switching duty cycle or frequency varies over a nominal range in relation to the ratio of the internal rectified DC voltage off the line and the desired output voltage. If you reduce the internal rectified voltage by using the dimmer technique this will drive the compliance of the switcher circuit outside its normal range. This could simply result in the output regulator just shutting off. On the other hand a different type of circuit may very well go unstable under these conditions and result in unpredictable output and possible overheating.

Is this what you're after? The outputs will be independent of each other. In your circuit, they would also be independent, but depending on the circuits cv1 and cv2, the voltages may not end up how you think they should be.

This circuit will work assuming CV1 and CV2 are just meant to receive voltage signals; if they draw current then the voltages will fluctuate. How much current will they be taking? And will it vary? You can add a couple of transistors if needed. I can give you the schematic for that if you want. But again, what transistors you need would depend on the current your CV1 and CV2 circuits will draw.

^{simulate this circuit – Schematic created using CircuitLab}

Also, depending on how stable you want the voltage to be, you might want another method. But I think this would be the cheapest way of doing it.