Is it possible to highlight part, but not all of something?

I have a part:
and let’s I want this highlight to only cover the bottom half of it. How would I do this? I first thought of just adding another part for the area I want to cover, but realized that won’t work for more complex shapes, like this:

You could split the model into 2 parts if it doesnt affect your scripts. Im sure theres no workarounds except creating a highlight for each part.

Splitting it into 2 parts wouldn’t really help in this situation. I wanted to be able to change what area of the part is shown in a highlight through a script, but splitting it would make me have to create a new part every time I want the shape to change. Also take into account that I’ve never been able to successfully use unions in a script.

TL;DR: I wanted the highlight to be tweened from the bottom to the top of the object with a script, so I can’t just split it into 2 parts.