When I found the solution to this, I was blown away by how simple it is.
So, you have an ISO file that you want to make some changes to, but you can’t change the ISO file because it’s like a DVD/CD where you cannot write onto it, no changes Master Miyagi.
What makes this particularly frustrating is that you can see all the files of the ISO, but if you just copy/paste them over into a folder of your choice, it doesn’t work.
The Solution (elegant I might add)
The solution is to use your extraction tool and just extract it to a folder of your choosing. I use the free version of winrar.
Right click -> extract files… -> choose destination -> voila!
Hope this helps!