Use bookmarks to divide sections of a song to select an individual part to practice. On currently released maps it could be "bookmark1 to bookmark2" but in future clients bookmarks can be labelled things such as "verse," "chorus," "bridge," etc. Individual bookmarks could be selected on a screen displaying the editor timeline after selecting the practice mod from the mod menu. I'm sure a lot of maps don't have bookmarks so red and green lines could have to do, especially on very old maps.