I was wondering if it's possible to change a celeron 366 mmc-2 with a celeron 500 mmc-2? or even to a p3 mmc-2?

To change? You mean to overclock? Ususally overclocking lets you get maybe 133MHz more out of your processor, but nothing is going to turn a PII into a PIII.

On the other hand ... if you mean is it possible to swap out processors in a computer. Well, that depends on the motherboard specs. PII motherboards are different than PIII motherboards - CPUs can't be swapped out.

It might be possible to swap a 366 celeron with a 500 celeron. Again, check the motherboard specs ...

Is this what you're asking?
I'm confused.