Mistwell
Crusty Old Meatwad (he/him)
Spell Versatility does not let you change spells that you get from a Subclass. Spells gained from features like the Divine Soul's Divine Magic, or any Warlock's Expanded Spell List from their Pact are not effected by it (even Mystic Arcanum spells aren't allowed, but that's a different discussion). We can safely ignore those origins when creating an ability that modifies the core Sorcerer Spellcasting by assuming that, while there are multiple different ways to trigger becoming a Sorcerer, being a Sorcerer is a thing that exists independently of however that switch is flipped. Which is the key thing that makes all Sorcerers into the same class to begin with, instead of the Subclasses each being their own unique class. This is backed up by the fact that once you become one type of Sorcerer, you can't also become a different type of Sorcerer, even when meting the requirements for it.
And you could say the same thing with Warlocks.
From the Sorcerer description (not a subclass):
PHB said:Sorcerers carry a magical birthright conferred upon them by an exotic bloodline, some otherworldly influence, or exposure to unknown cosmic forces. One can’t study sorcery as one learns a language, any more than one can learn to live a legendary life. No one chooses sorcery; the power chooses the sorcerer.
Magic is a part of every sorcerer, suffusing body, mind, and spirit with a latent power that waits to be tapped. Some sorcerers wield magic that springs from an ancient bloodline infused with the magic of dragons. Others carry a raw, uncontrolled magic within them, a chaotic storm that manifests in unexpected ways.
The appearance of sorcerous powers is wildly unpredictable. Some draconic bloodlines produce exactly one sorcerer in every generation, but in other lines of descent every individual is a sorcerer. Most of the time, the talents of sorcery appear as apparent flukes. Some sorcerers can’t name the origin of their power, while others trace it to strange events in their own lives. The touch of a demon, the blessing of a dryad at a baby’s birth, or a taste of the water from a mysterious spring might spark the gift of sorcery. So too might the gift of a deity of magic, exposure to the elemental forces of the Inner Planes or the maddening chaos of Limbo, or a glimpse into the inner workings of reality.
Sorcerers have no use for the spellbooks and ancient tomes of magic lore that wizards rely on, nor do they rely on a patron to grant their spells as warlocks do. By learning to harness and channel their own inborn magic, they can discover new and staggering ways to unleash that power.
That description simply does not mesh with changing your spells overnight. Particularly not given the fact all campaigns thus far have assumed as part of that setting that sorcerers couldn't do that - by definition. I'm going to need some explanation that's better than what's being offered so far.