You can use either a local variable or value property node to set a control value.
Right click on the control and Create/Local Variable or Create/Property Node/Value. Change the property node or variable to write mode by right clicking on it and selecting "change to write". Local variables might default to write (can't remember) but I know that property nodes default to read mode.
I prefer property nodes simply because they have an error in and out so I can control the flow.
[Edit:] Don't forget that you must have switching instead of latching for the mechanical action. If you need a latching boolean control and need to programatically set it's value then you will have to reset the state after you read it using either a local or property node.