I'm really not sure about access from the inside, it would make it a lot easier if you could. The problem is the pins have little metal barbs to hold them in and they rust to the panel. Maybe get some tooth floss or fishing braid and work it under the badge until you have identified where the pins are then slide something flat under on both sides of the pins and gently lever them away.
That being said see if you can get new badges from Nissan etc first then you dont have to worry about how the old ones come off

I cant believe I never looked at that thread! top effort there!