I'm getting ready to sell my old house, down to the final handy-man type
fixups. One problem is the ceiling tiles in the basement. The house is
50 yr old and I suspect these tiles have been there for a good portion
of its history. The tiles are those square ones the consistency of
heavy cardboard, with the little patterns in them, about 10-12" square.
Several have been knocked off/removed during renovations, several are
sagging down (I think dislodged when the electrician was running wiring
above them) and a few have water stains from an old leak.

Warning - completely NON-DIY'er here... I found a box of replacement
tiles. Is this something I could do myself? How are they held up? Could
I get away with like super-gluing them in place? How to get the sagging
ones down? Just cut? This is primarily in the back utility area of the
basement, so while I want it to look good, I'm not hugely concerned
about aesthetics... more wanting it to look well maintained.