Not an easy way, but I received the following from an ESRI tech. Essentially this enables you to create a new site without reinstalling:
1. Stop the ArcGIS Server Service in Windows Services.
2. Delete the following files from c:\program files\ArcGIS\Server\Framework\etc :
a. arcgis-logsettings.json
config-store-connection.xml
b. machine-config.xml
3. Rename the c:\arcgisserver\config-store folder to something like oldconfig-store
4. Start the ArcGIS Server Service in Windows Services.
5. Log into Server Manager and choose to "Create New Site"
6. After you are back in Server manager, stop the ArcGIS Server Service again.
7. Copy everything from c:\arcgisserver\oldconfig-store to c:\arcgisserver\config-store except for c:\arcgisserver\config-store\security.
8. Leave the new c:\arcgisserver\config-store\security folder alone when you copy the information back.
I was given this info, but haven't test it yet.