In MHRP, this requires achieving a Milestone (ie resolving, one way or another, a character "arc") and then using those XP to buy the appropriate new power set, distinction of whatever.I don't hold it against the game, but it made me think about the necessity of having rules that make thieves be good thieves and bad sorcerers.
10 XP for finishing a Milestone will allow meaningful change but not a complete rewriting of the PC. We've seen this in our MHRP/Cortex+ Heroic games, but I think not to the extent of change your character was undergoing.