There are two very different issues here:
On the one hand, people will say “You can’t white balance an image after it’s been interpolated.” This is not true. Whether you interpolate using UniWB or else use the actual white balance that you want the final image to have, as long as the image is still in the camera input profile you can change the white balance after it’s been interpolated, the colors will look just fine. Occasionally I have found it convenient to white balance an image after it’s been interpolated instead of before, for example when the lighting was mixed and I wanted to apply two different white balances.
On the other hand, not white balancing before interpolating can produce artifacts, which I didn’t realize was the case. The artifacts aren’t always obvious. My studio lighting, such as it is, is tungsten lighting, and when using tungsten white balance the artifacts from not white balancing before interpolated are not very noticeable. But if the desired white balance is daylight white balance, the artifacts are considerably more noticeable.
So at 400% zoom for tungsten white balance, I ddin’t notice anything amiss until I had the “white balanced before interpolation” image to compare to the “white balanced after interpolation” image. But at 400% zoom for daylight white balance, the artifacts are glaringly obvious.
I’m guessing it’s the high red multiplier required for daylight white balancing that is key? But this is just a guess. Maybe there is a pre-interpolation white balance that is ideal regardless of the desired output white balance? What about images shot under completely overcast skies vs. images shot under daylight/sunlight? As I don’t know what causes the artifacts I’m not able to generalize.