Cutting disc on a grinder works really well. The butt cap may not come off if it were paste epoxied like the rest of the cork. You could buy another one, but it may take some work to get it to fit. If you want to leave it as is after cutting, you can sand down the cork you cut (the drop) and mix with paste epoxy or glue and fill the blank void with this. Or wrap the new end of the butt with tape (creating a cup), and use this cork/epoxy mixture to make your own butt cap.