Vob Blanker allows you to change the program that plays on the menu when you select it. Say you have the menu from an official DVD. You want to change make it play your version when you select "play movie". What you'd do is author a temp DVD with only that one item in a particualar title. Then you'd use vob blanker to change the ifo assoicated with the "play movie" function of the original DVD.
With PGC Edit, you can change what the buttons do and re-arrange things. You can add new buttons to the menus as well I think.