It's unfortunate this design sacrifices elegance, flexibility and function to a gimmick—one that amuses some, but likely lost on many. It is possible to modify, rename and move buttons in the Playlist section, but that requires leaving Playing Now and it still more cumbersome and confusing than it need be. It sacrifices entirely the possibility of attaching a particular set of rules (i.e., a smartlist) to a button, and then being able to provide or change the text 'seed' with every use. For example, having a button for 'highly rated, good quality Rock', and then being able to seed that with an Artist, Style, Year, or whatever.
This may seem like an obtuse criticism for those who are just trying this out. But consider what happens as those buttons fill up over time. Due to the lack of flexibility, they become subtle variations of one another. Even in the unlikely even you can label them concisely and remember what they do, you'll soon run out of buttons. Why can't we enter a seed in the text box and then click a button to combine that with the rules set for that button? Or right-click a button to change the seed and/or modify the rules? Why can't we reorder the buttons by dragging them? Why can't we (optionally) have the buttons appear in any view? Because that's not how a car radio works, and users prefer gimmickry over elegance.
