What are you trying to do in the end? Are you trying to set the resolution in WinPE during deployment, or set the resolution of a Windows 7 image that you just put down?
Setting it in WinPE: https://technet.microsoft.com/en-us/library/ff716217.aspx
Setting it in deployed Windows Image: https://technet.microsoft.com/en-us/library/ff715801.aspx
If the machine is already imaged and you are trying to do it as part of some SWD task or something, then I'm not sure. Hopefully the above should help. You can set it in the unattend.xml file and use Provisioning to inject that unattend file.