Wouldn't it just blow their little minds if some day in the fleamarket or as an event there appeared a "blue" grocery bag labeled "a different type of grocery"?
Tee hee!
Changing a bag to blue should be a simple enough mod, but alas we wouldn't be able to change the label.
Their proccupation with the fact that the house was empty before can also get a little wearing. The house was only empty for the very first generation. Depending on which generation you're at it's likely it was a several-greats grandparent who discovered the house; since then it's been inherited from one of the current peep's parents.