This is a question many time asked by SP3 owners that want full access to Power Plans. Before I show how to do it I should add that tweaking the Power Plans may have a negative impact in the battery life. In another hand Connected Standby is one of the best features added to this device. It's the feature that allows you to still receive emails and other services while the SP3 is in Standby.
To disable Connected Standby you should open the Registry and change it:
HKLM\System\CurrentControlSet\Control\Power\CsEnabled (From 1 to 0)
If your want to revert it back then just change the value to 1. After each change you need to restart the Surface Pro 3.