I'm not sure if you were around to watch the NBA in the early 80s, but there is no doubt in my mind that Magic could have been listed at and succeeded at any position on the court. Magic had all the skills needed to play any position on the court. I would lump Bird in there as well, except he wasn't really quick enough to defend guards on the perimeter (or forwards on the block, for that matter). I didn't make any comments about how he did in that game 6, just that he started at center on the night. I remember watching it.
As far as Diaw goes, he is another excellent example. Whether or not he is good or not is immaterial. The fact that he has a skill set that allows him to play PG and/or C is the point. Not sure if you play fantasy basketball, but Diaw qualified at PG, F, and C as recently as two seasons ago in Yahoo leagues. Not sure about last year.
On a much lesser scale (say take it down from Italia Serie A to Viet Nam division 3.16) I played both PG and C in high school. I grew seven inches before my senior year in high school and played Center on defense. I didn't lose any coordination during my growth spurt (didn't have much to lose, I guess) so continued to play PG on offense. So it is possible, without question.
Once I scored a basket that still makes me laugh.