-Well, since most of them are made with RPGMakerXP, why not use that?
-This is taken from the usage notes section.
"First, make a copy of your entire projects folder. Then go into your games Data Folder. Copy over all of the Map Files, MapInfos, and the Tilesets data files.
If you used any custom Tilesets or charsets or even pictures copy them over too, same for audio.
Then go into the merged project and make an event and make it control switches. Then copy all of your switches from your game to the merged project."