Okay, I'll take a stab at this. I'm doing exactly what you're talking about, on a slightly larger scale, in my current project. So, I have a "chapter" variable, which goes up when you do certain things.
Then, on a given event, such as an NPC, I create several pages. The later pages have conditions such as "Variable: Chapter=2 or more." On those later pages, I change the graphic, as well as what the event does. Sometimes there's no graphic.
So, there's an event in your house that is the NPC of the player's mother. Once the chapter is 2, the event goes to the next page, which has no graphic. Look, mom's not home!
Outside, there was an event that was a blank graphic on Chapter 1. But hey, now it's chapter 2, so it's on the next page. Look, here's mom!
I'd post screenshots, but I have to go to work soon. If I'm too confusing now, let me know, and I'll post 'em.