"Mazda Miata 2000 has pcm that should be replaced, in order to turn off the check engine light. The car runs good, but can I do any damage it I do not replace the pcm?"
Ok, you'll have to clue us in on why the PCM needs replacing?
Have you had it scanned for trouble codes? If so, what were they?
My crystal ball is in the shop, so I need to know some things to help.
"Mazda Miata 2000 has pcm that should be replaced, in order to turn off the check engine light."
Never. That isn't how the PCM works.
If the problem is resolved, the check engine light will go out. In rare cases, the PCM may have to be replaced, but usually the engine won't run when that happens.
Please, get the thing scanned for trouble codes and let us know what they are. Anyone who tells you that the PCM needs replacing, just cause the light is on isn't very knowledgeable.
Let us know the codes.