I just wanted to say that I think @TrevorFedyna 's solution is the best way to solve this.
If you really wanted to try using the EMS, the easiest way to do it is probably using the OpenStudio SDK inside a GHPython component to edit the OSM like you see here. However, for a case like this, I’d be worried that you get some positive feedback loops that result in extreme or unrealistic ground temperatures, especially for unconditioned spaces. You could imagine a scenario where the temperature in the Room drops, so then the temperature of the ground drops, causing the temperature in the room to drop further, and so on…