Is it possible to replace bearings in Shimano XT bottom bracket cups? Curious if I can just replace the bearings in my existing cups or if I would need to buy new cups?

If possible to replace them then what are possible high quality replacement bearings?
It isn't recommended by Shimano, but some shops use a bearing puller to slide them out of the bottom bracket. I don't know if Park Tool makes one, but you should be able to find one at a specialty hardware store. Once you get them out, you can service or replace them.