cmd# regedit.exe /s path-to.reg
See:
A .reg file has the following syntax:
RegistryEditorVersion Blank line [RegistryPath1] "DataItemName1"="DataType1:DataValue1" DataItemName2"="DataType2:DataValue2" Blank line [RegistryPath2] "DataItemName3"="DataType3:DataValue3"
[-HKEY_LOCAL_MACHINE\Software\Test] [HKEY_LOCAL_MACHINE\Software\Test] "TestValue"=-