You can now update the sandbox server client. It should be online soon. You can test both HE and SPG changes in it. They will likely be implemented this year.
Download size (SD): 81.60 MB
Installation size on computer (SD): 177.44 MB
Download size (HD): 101.66 MB
Installation size on computer (HD): 222.87 MB
The sandbox can only be downloaded through the WGC.
If the sandbox is already installed, just update it.
If you have WGC but don’t have sandbox installed, use this code in WGC:
All games → Install the game by ID