Okay, confused :roll: They are on the frame anyway
Short of clear coating them and even them I think you will find them very fragile, just be careful around them
Just found a set of Original GT decals that I have, basically they should have had a paper application tape over the face of the decal, this is enough to lift the decal away from the backing paper to reveal the adhesive back of the decal, this is rubbed down on the frame and the application tape removed leaving the decal in place
The paper application tape is prone to going off with time, so I would guess the seller has removed it to improve the look of the decal when selling it, it should have had the tape applied before being supplied to you, to help you fit them
They should be more durable than a waterslide but over time the glue deteriorates and hardens, if you warm them up a little the glue should soften and improve a little
Basically leave it next to a radiator overnight and them just give them one last "careful" rub onto the frame, cover with a sheet of paper and work over the image with your thumb applying even pressure
Hope this helps