I am trying to change the active SDK path because we need to put it under source control.
In the Preferences page, I added our custom SDK path to the "Simplicity Studio -> SDKs" setting page and unselected the default path:
After applying changes, the new path is successfully used in my project.
Unfortunately, after I close and restart Simplicity Studio, the default path gets selected again automatically and my project now uses the default path:
How can we prevent the default SDK path from being re-selected automatically without having to uninstall it completely?
That looks pretty frustrating, and is a surprising response to your attempts to change the SDK location. As far as I can tell, you are doing it as described in our AN1160: Project Collaboration with Simplicity Studio document.
Studio may be preferentially selecting the SDK in the default location, which I see you still have in place. I recommend moving it somewhere else on your drive or deleting it, restarting Studio, and then selecting the path you want to use.