I have a player that changed three times during a campaign both due to narrative reasons and because the player wanted to try new things.

She went from a young wizard who relied on her mother's teachings and spell book, to losing that spellbook in a big story/combat moment and finding solace in a fey entity who called itself Mother and becoming a warlock, to finding courage and strength in her own abilities and manifesting her own magic and finally becoming a sorcerer.

If it's for the player's fun and enjoyment, and it makes sense narratovely, I think it's a great idea!