Can you share also how you’re implementing Storable? That implementation is really the key to evolving the schema. All you’d need to do is to ensure that your Storable implementation works on both the old schema as well as the new schema.
By the way, I don’t know how big you expect your dataset to be, but if it’s early in the project, I’d consider using the event log pattern as is currently being done with ckBTC. It should give you a lot of flexibility to evolve your schema in the early days, then once it’s established and you need to scale, you can switch to using stable BTreeMaps.