To glue, or not to glue

[PbFut]

Yesterday I removed the headliner and sprayed on some left over thermal Lizard Skin on the roof. After removing the headliner, I noticed a dried red colored adhesive that shaved right off. I am not sure if it was factory or someone's attempt at smoothing the liner. Does the liner normally need an adhesive? I was able to smooth the liner backing board with descent results. The lizard skin is a bit bumpy so adhesive may be challenged or I'll have to sand and knock down the high spots some. I don't want to redo later as that trim was impossible to remove without snapping a few tabs. So as the title asks, glue or no glue? or maybe velcro? What's your opinion?