Well, i just tried it on mine. I took a 32.768MHz crystal from an old serial mouse, and the result was: It didn't work. The player just didn't do anything.
Then i tried one from an old electronic watch, dunno what frequency it had, but surely lower than 24MHz. It didn't work with that either.
Strangely enough, the watch worked with the 24MHz crystal from the player, but i didn't really keep it running to see how much would the time be off.
So in the end i called it quits for now and installed the 24MHz crystal back into the player, running happily again.
I think i need a crystal with a very close operating frequency to the original one, say, a 24.576MHz one from an old TV game or something. Now i know for sure that installing a crystal with a very different frequency won't harm the player, just that it won't turn on anymore till the original one is back in place.
I'll see what else i can dig up and report the results. :P
But feel free to try it yourself in the meantime.