Replace screen taps w/pot Zenith

[TinCanAlley]

I've been looking over the schematics for my zenith and it seem that the hi tap is straight through, the medium tape gets a 2K resistor and the low adds another 2K resistor for a total of 4K. Since this setup really doesn't allow for fine adjustments in the grayscale setup (I still see a faint amount of red in the bright areas while watching B&W), would it be possible to replace this setup with a 4K pot for each color?

Thanks!