Once you get the CSV of the customers and assuming you are using the latest FA v2.4.3 and the sql/en_US-new.sql Chart of Accounts, manually enter one typical ustomer and see the diffs in the before and after backups and construct your sqls accordingly. This will need to be carefully done in a cloned container and then migrated to the production install. The same can be done for vendors (suppliers), items (inventory), etc.
Try to revert to an earlier version of DacEasy before Sage took over. You will most probably find a non expiring version.....MBAs tend to enforce migration by such blackmail tactics - they probably cannot survive in a non-monopolistic environment - they will however wax eloquent on the virtues of their idea of a free "market economy".