I figured out a way of using vectors of different lightness in conjunction with a gradient map as a filter mask to create a clipping mask that works as a transparency mask in Krita, so that I can basically use vector transparency masks for screentone values, which simplifies my workflow in the long-run as it means I can easily change any fill at the drop of a hat without needing to redo a bunch of fills painstakingly by hand.

Huge improvement in speed.