The "current" DOP network is the network the shelf tools put new nodes into. The user can change this using the simulation menu in the bottom right corner of the main window. This method lets you programmatically set the current simulation network.
Because the current dopentwork must always be writeable, setting this to a non-writeable dopnetwork will not cause hou.currentDopNet() to change. However, it will update the current dopnetwork for the purpose of other UI, such as the blue cache bar, provided the node is a valid dopnetwork.