I do not think you can modify group policies from the command line. But, you can modify registry keys using the
reg command. Most group policies have their corresponding value in registry.
Go to Start -> Run -> type cmd
Adds, changes, and displays registry subkey information and values in registry entries.
reg add KeyName [/v EntryName|/ve] [/t DataType] [/s separator] [/d value] [/f]
Copies a registry entry to a specified location in the local or remote computer.
reg copy KeyName1 KeyName2 [/s] [/f]
Deletes a subkey or entries from the registry.
reg delete KeyName [{/v EntryName|/ve|/va}] [/f]
Returns a list of the next tier of subkeys and entries located under a subkey in the registry.
reg query KeyName [{/v EntryName|/ve}] [/s]