There are three competitions at a sanctioned IBDA race. Races are held in the stock and modified division, and at the beginning of the races there is the best decorated competition. Winners in each of these three catagories is entered in that years Worlds Finals. Stock sanders are straight out of the box, with no mechanical alteration being done to them what so ever. They are allowed to have wheels and other guides mounted to them to help guide them straight down the track, and of course they can be decorated.
Modified sanders are a totally different story.
Modified are the ones that have had the gears changed, motors altered, and goodness knows what else. The only two rules regarding the modified are that they have to be powered by 110v and that they run on an unaltered, store bought abrasive belt. Apart from that you can go nuts, and many of the modified entrants do. The vast majority of entrants in our races have decorated their sanders in one way or the other. Decorating is allowed in either category, and does not affect weather a sander is stock or modified.