PET:Polyethylene terephthalate (aka PET, PETE or the obsolete PETP or PET-P)
I want to keep my guitar in a good condition. Will the adhesiveness damage the fretboard or guitar finish?
No worries, the adhesiveness will not damage the wood or finish of the guitar.
Some time later, I may consider replacing the sticker with another design. Is it difficult to remove the stickers and also any any adhesiveness will be left behind? You can peel off the sticker easily when you want to remove it. No adhesiveness will be left behind usually. (If the stickers have been applied for years, there will be little glue will be left behind.)
There is laminate transparent layer on the top to respond to a variety of cases from its flexibility (playing style, strings, condition of fretboard).
When it begins to come off, please remove it. It doesn’t matter about its quality and the durability.