Yeah, just right-click your union and press “Export Selection…” This gives you an .obj file which you can reupload as a mesh.
This isn’t really much more convenient than the recovery process, so it might not be worth the effort. You might want to look into making meshes from scratch, since most 3D modelling software has similar tools to Roblox’s union system. For example, in blender, the Boolean modifier can subtract (difference), union (union), or keep only the intersection (intersect, not something supported by Roblox I’m pretty sure).
Edit: Looks like my image is getting cut off, but if you click it then it should show up properly.