A coworker of mine recently had a need to unconstrain a lot of walls in his Revit model. Naturally, we turn to Dynamo to get this done. Initially we thought it would be as easy as assigning "Top Constraint" as nothing or unconstrained. Wrong! It turns out, if you want to unconstrain a wall's top, you simply set the value to the wall element. Check it out in the video below!

First I demonstrate what I tried at first, then I show the solution.     Have fun and be in awe of the mysteries of Dynamo!