As a Roblox developer, it is currently impossible to change the class of a an item in the Roblox Studio explorer and have all the properties and children be moved over. This could be UI objects being converted to another or even a normal part to a meshpart if I ever wanted to add detail to part of my map without the size changing.
If Roblox is able to address this issue, it would improve my development experience because it will help me make games faster if I ever make edits in the future. At the moment, the only workaround for this is to make a plugin that does this or insert a new instance and manually change each property, which I find myself doing a lot.