That custom control editor is one of the more arcane parts of LabVIEW. It exists since at least LabVIEW 2 and has seen only small improvements since. And according to its original creator back at that time it is a pretty nasty piece of software code that would need a complete rewrite to be able to make more elaborate modifications to it. Chances for that to happen are about 0.0something % nowadays. Unless someone somewhere is willing to pour a few millions into this. 😎