This question was floating around a plurk so I thought I'd ask here - can characters learn certain magic/powers/abilities if there wouldn't be a restriction to it based on canon?

Like, take Harry Potter magic. Canon shows that there is some biological element to that. So I can see never being able to learn those spells.

However, a series like Yu Yu Hakusho and some others specifically show in canon that the "magic" they use is actually just harnessing spiritual energy that everyone has inside of them. For canons like that, would it be possible for mundane characters to be taught any new magical skills? Or could characters with some magic in canon expand their skillset?