the general way to "SetPatch" from one of your plugins is using IHDEHost.SendXMLSnippet.
but as you can see on the IHDEHost methods overview page it also has some more convenient methods to use for: SetComponentMode, ShowGUI, ...the latter being probably what you're looking for, even though it seems we're lacking an option to HideGUI...
if i understand this right, i'm afraid this may not exist even though there is IHDEHost.GetXMLFromSelection but that will only give you the current selection.. but then also i am not sure what it would have to do with your initial question to set the visibility of a ui-plugin!?
in general you can definitely argue that the api here is not very well organized. it more-less grew with our needs at the time but not much further to full consistency.
regarding SendXMLSnippet also have a look at https://github.com/vvvv/vvvv-sdk/tree/develop/vvvv45/src/core/Hosting/Refactoring where you can see it in use.
hope some of that helps..