I wasn't looking to keep mine when I pulled it, due to cutting the top open. So, I just pulled carefully.

It did leave some foam residue on the metal. Some bits of the glue still holding and the headliner seperating a little behind the visible layer.

If I were to keep, I'd try a plastic mud knife, or maybe a plastic body filler "scraper/spreader." Use it to coax the seperation. I think if you simply pull, you'd end up stretching the liner to the point it might not go back in cleanly.

Big Truck: 00, 3.5, Endeavor, 5-Spd drive line in hand!
Little Truck: 87, 2.6T I/C, MT, LSDs, Tonneau Top
Her Truck: 03, 3.8, 20th Anniv, 65k
Daughter's: 06 Eclipse, Keeping it Mitsu!
FSMs: MitsubishiLinks.com