If you work with CSG and physics, you probably already know that ROBLOX doesn’t use the exact geometry of the Union for collision, rather it uses approximate convex decomposition. While ROBLOX has an option for toggling this in the physics settings, it only applies to newly inserted Unions.
Overall, toggling between these options isn’t very fast, and I was pretty annoyed by this. So after I discovered that we can actually access ROBLOX Studio’s settings from plugins, I decided to make a plugin for it.
Unlike the default functionality, this plugin actually updates the geometry of pre-existing unions. It also updates geometry when the CollisionFidelity property of a Union/MeshPart changes.
You can get the plugin here:
Hope you enjoy it 
P.S.
- This also applies to MeshParts!
- This plugin is actually an extension to the functionality of the decomposition geometry, while the plugin button itself is just a quick toggle for the setting. If you toggle the setting manually in the physics settings, you’ll notice that the plugin button will reflect its changes.
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In order to “update” the geometry of a part, the plugin will change the parent of the part to nil, and then immediately back. This could cause problems if you are using joints. I’m probably going to add a safeguard for this soon.
EDIT: This is no longer the case. @TheNexusAvenger noted that I could update it by just bumping the Transparency.