Single level boss problems?

I'm almost certain this question would have been asked before but for the single level option in a newer patch will you make so bosses play the same as in the actual game. And will you make so that you can continue on rather than quiting straight away so that you can see the super secret levels whenever you want (dont put them in the single level option because people need the surprise). And also will you make so you can hear the music for that level rather than random music. In fact keeping that in mind i was actually thinking you could make different music for each level rather than each world, although i can understand if you dont want to do this.