With IPv6, it's common to have multiple addresses on an interface.

So on options is to assign yourself an [RFC 4193](https://datatracker.ietf.org/doc/html/rfc4193) fc00::/7 random prefix that you use for local routing that is stable, while the ISP prefix can be used for global routing.

Then you don't need to renumber your local network regardless of what your ISP does.