On no!

To weld in a new roof skin you will be removing far more than an ABS head liner. A roof skin isn't just a job that anyone can do and do right.
Im asking about the headliner so i could remove it and try popping out the dents from the inside. If that does not work, I would replace the entire roof skin. I understand that it would be a lot of work, but thats not why I'm asking about the headliner.