It may be difficult to find one that isn't flat and has a curved key top. If you find one, then I believe then I think that it is likely that it has the wrong height.
Most keys on POS keyboards are flat and wide, and made to be relegendable, with two parts: a bottom and a flat top. The top is either clear for showing a piece of paper underneath, or opaque with a printed generic label.
The POS brands with Cherry keys that I know of are Tipro (low keys), Jarltech (somewhat low keys) and Access.
You may find relegendable keys also on some keyboards from Cherry (high keys) and Genovation (high keys).
Another thing is that you would have to disable the key somehow. If your keyboard has NKRO then maybe you could do it in software.
To do it in hardware is more tricky. You would have to open up the switch and cut down the sliding part that touches the metal "leaf" and put a spacer inside the switch to keep the "cross point" apart, because the slider does not do that any more.
I would also advice you to replace the springs with weaker ones. A key with two switches is much heavier.