They are plastic welded together...so they don't just come apart. In order to separate them, you would need to separate the plastic spot welds. And then you would need to plastic weld them back together. Not something I would probably try to do myself, because I have no experience with working with melted plastic.
I've worked with the plastic welds before. I was recovering some door panels on a 95 Civic. All I did was take a soldering iron to the plastic spot welds, and once it starts to get soft, just pop them through. If you have an extra junk door panel that you're working with, I would cut off some of the plastic from it to use when you put the panel back together. Just do it as if you're soldering plastic. It's not that bad.