Update/Delete custom object activity log

Recognizing that this might be difficult to accomplish for Marketo - from the user's perspective - it's kind of like saying "I'll build a door so you can enter the building!" "Oh, you want a door to leave, too? We don't offer that." The use case I'm working with is a company whose clients are businesses that own private aircraft - usually more than one - and various contacts within the companies are associated with the aircraft. The custom object is the aircraft and it can have lots of different key attributes like "model" or "weight class." And demographic scoring is based on whether a person is "added to" an aircraft with these characteristics. For example, Added to Aircraft->Weight Class is Heavy is worth more points than Weight Class is Light. But we want to be able to deduct points if the person is removed from the Aircraft with Weight Class=Heavy. The workaround in place is to completely re-score (demographic scoring) the entire database once a week. It works - but yuck!