you can use RDP Wrapper which acts as a middleman between Terminal Services and Service Control Manager. This way you don't need to touch termsrv.dll file...
Download and extract RDPWrap-v1.6.zip (or newer), then run install.bat as admin. After installation is completed, run RDPConfig.exe. If all items under Diagnostics are green, you should be good to go.
Multiple RDP (Remote Desktop) sessions in Windows 10