How could the purple shape be cut horizontally at specific/variable heights?
Meaning, the top and bottom of the purple shape are fixed, but the edge loops in between need to be at varying heights, so not equidistant from top towards the bottom.

Try one of these nodes.....Knife, Clip, Polysplit, Polydraw.

If you wanted to "split/cut" the geometry into 2 parts you could also use a flat grid as a cutting
plane and a Boolean set to shatter.

The knife node was excellent, thank you!