First of all thank you to Tammy who showed me this trick as I had spent ages trying to figure out how people were doing this and Tammy knew how to do this and modified a screen of one of my worlds and I spent a week thinking I had done something in Unity and was confused how it looked so perfect.
The first thing you need is obviously terraformer permission so assuming you have permission already you will need to open up the AltSpaceVR menu which is the green triangle on the left-hand side of your screen.
Entering the purg command and clicking that triangle button will enter you into the loading screen.
Editing your loading screen
Editing your loading screen is a bit buggy as it’s not an instance that is fully working because one thing you cannot do in it for example is talk to other people. However, if you have the AltSpaceVR voice translation contextual permission enabled you can still talk by text inside this realm.
Besides that, it is pretty much like editing any other space however weirdly enough the projector won’t be heard inside the loading screen but if the projector is in the loading screen instance you can hear it but can’t see the stream in the main instance.
Practical uses for editing your loading screen
You can use this to your advantage especially when you are hosting events. You can add loading screen information about your event or add a logo or create a themed loading screen in line with your world/event.
Some people add cameras so that people in the main instance can see who is coming into the world before they are loaded in which is faster than the doorbell MRE.