Data Migration testing Cycles in S/4 HANA Public Cloud

With only 2 environments (Q & P) available for S/4 HANA Public Cloud, how can we manage multiple (1,2,3...) Data Migration Testing cycles in Q environment without data purging/ system refresh. What is SAP's recommended approach to this?

How do we conduct Mock Data Cutover (Dress rehearsal) where we test the full scale data migration for Master and Transactional data as Q system already has data loaded from Trial Migrations.

How to we manage data migration for Open transactions across Trial migrations (1,2,3) for scenarios where open objects loaded from Trial Migration 1 are still open and part of Trial Migration 2 load. This is specially for transactions having longer cycle time.