I just got FIFA 2000:MLS US version, and Brasil 1970 has Pele listed as No. 10 just like they have Ronaldo listed as No. 9

Yes, and that's probably because they didn't buy the rights for his name either. He is also No. 10 on Cosmos 72-75 and Brazil 58. Who cares? I'm not going to complain about his name if he has a perfect set of individual stats.

Go to edit player and change his name.