Slots get re-negotiated every day. It's no big deal.
Many controllers will help out an aircraft or pilot in many ways if no one is inconvenienced and no rules are broken - using a non-duty runway, sorting out a higher initial level for a positioning flight so that the aircraft can go up like a rocket, flying over a kid's party, taking a look at a house a pilot is thinking of buying, checking out how busy the golf course is on the way in. Done them all - without any problems.
But to knock on anything but the flightdeck door for anything but a professional hello is something that only a @rse would do.
But unfortunately, just as in any other walk of life, there are a few @rses in ATC.