In article ,
"Andrew Mawson" writes:

The conventional way of fixing them was five dabs of adhesive ( each
corner plus the middle). If the ceiling had previously been painted
they will probably come down pretty easily with a paint scraper, as
the paint pulls away from the plaster. If it is old enough to have
been painted with distemper they will practically fall away.

Many years ago as a teenager, I put these up in my bedroom in
my parents house. However, budding diyer as I was even back
then, I did it properly, fully glueing the backs of the tiles.
More recently, my parents went for a major redecoration of my
former bedroom (not DIY). The builder tried to prise one or two
tiles off, and quickly decided it was faster/cheaper to bring
down all the plasterboard, fit new, and reskim.

--
Andrew Gabriel