RpR is right grafting onto it will still give you a large tree but you can keep it at a manageable size with pruning. yearly pruning is a must to keep it small. if you skip a year it will get away from you you'll have to remove large limbs which isn't good for trees. Grafting a columnar apple on it may be a good idea as they don't do too much branching and tend to grow more vertically.
