Unlike just muting parts completely, there isn't much you can do to make a 'busy' part simpler, short of completely editing the style and putting in a part of your own... most of the time, you can't simply erase some notes from a busy track and get a simple one.

However, if the drums and percussion get to be too much, I guess erasing a percussion part or two might be fairly simple... lose the bongos or congas and shaker or tambourine might help thin things out a bit. But simplifying a busy guitar track piano part or horn parts would be a major undertaking.

Another place to look would be translated styles... Perhaps you can find similar styles that have simpler parts coming from other arrangers (personally, I find a lot of Roland styles to be not too busy) and either use the translation whole, or merge it with your favorite tracks from an existing Korg style, for a hybrid style. If the OS makes it easy to do (the Roland's do, for sure!), assembling new styles out of Parts from other styles might be a far easier task than creating your own styles.

Just a thought.