I've searched the internet through 30'ish thread / forum posts and cannot find the answer to this.

I just completed all 5 campaigns and want to go back to chapter 1 to change some plot decisions. I get that I have to finish chapter 1 for the change to take effect but what happens to chapters 2-5?

Also does this work exactly the same for all other TTG's such as Walking Dead?

Thanks as always, love my Gog!

You have to replay everything from that point on.
I think it's the same efor the other Telltale games too, I didn't try it for the other ones though.