You can make the NS record for the _acme-challenge.domain.tld point to another server which is under your control, that way you don't have to update the zone through your DNS hoster. That server then only needs to be able to resolve the challenges for those who query.
Alternatively you could use Continuous Archiving with Point In Time Recovery [1] which has been built into Postgres for a while. Once your db exceeds several tens of gigabytes dumping to SQL is just not a viable solution anymore.
