Is there a way to have all custom properties closed instead of expanded by default? I’m adding lots of custom properties and it gets pretty messy pretty quickly with them all expanded.
Not currently.
Tiled doesn’t currently store the expanded/collapsed state of properties at all, so even if you collapse them manually, they reopen when you switch documents.
Yeah I know… Annoying 
. Can you get to that through the plugin API. I don’t know if plugins can get to the underlying widgets
Scripts don’t have that kind of access to the widgets.
I don’t know about C++ plugins, but since C++ plugins have to be compiled along with Tiled anyway, you might as well fork Tiled and maybe fix the issue with property state not being saved xP