Is it possible to modify the Subscription job to check for a different property than "Mark page as changed" if it should add a page for the next subscripton mail?
If yes a few pointers or a small example would be nice :)
It is not an easy fix...
The reason is that the method EPiServer.Personalization.SubscriptionJob.GetChangedPages is using a stored procedure to quickly identified changed pages.
You can study the code with Lutz Roeders's Reflector. Just load all assemblies in your EPiServer bin folder and search for the class SubscriptionJob.
One possible approach is to use on of the EventHandlers on DataFactory to catch the page before it is saved and add you own logic that updates the property "PageChanged" when your criteras is fullfilled.