Hi Eris,
I'm not saying Ysl's suggestion is not reasonable. I'm just saying WACUP provides other default ways to restart a song. Also, it is possible to reconfigure the previous button, so that it can provide a restart function. IMO, this is both the good and bad of WACUP (and Winamp for that matter), there are many different ways to do stuff and many configurable options that let the user change how stuff can be done.
Have you right-clicked on the previous button? You should get a pop-up menu with a lot of commands you may find useful. The first command listed (Previous) is what is executed by default when you left-click on the button.
