Can the DITRA-HEAT-E-WIFI be installed to replace an existing Schluter Thermostat? Can it be instlalled to replace a non-Schluter Thermostat? How is it installed?

Yes, the Wi-Fi thermostat can be used with any electric radiant floor heating system that does not exceed a 15 amp load. Consult with a local electrician to ensure electrical specifications are met. Other than a Wi-Fi signal and a router with good connectivity, there is no additional hardware required. The same line and load principles exist.