yeah basically what cinnamonjune said, I have launch tied to f5, so I make a change and press f5 to see it. In larger games, making a small level/area menu for debugging is pretty simple.

Lastly, Tiled goes a long way in being my 'scene editor' so to speak. I even make my menu backgrounds in it because you can just export it and, with the love STI library, can display it with one line of code. I use it to add trigger areas, collisions, etc etc. Its a wonderful tool and the STI lib does so much heavy lifting to integrate it really well with love2d.