No, individual sites cannot be moved. 

If a site's sensors need to be associated to a different account, you will need to uninstall the sensors, create a new site in its new account, and redeploy/reconfigure the sensors under the new site. 

If the historical data is important to preserve, there are two options. One way is to manually export the data to a .CSV file from Energy Time View prior to the uninstallation/site deletion. Second option is to uninstall the sensors but NOT delete the devices. Leaving the devices intact with no sensors will maintain all historical data.