Can I change anything while the migration is running?
Once you started the Full Data Migration, the best idea is to just leave it. Make yourself a cup of tea while we’re transitioning your records.
Don’t change or delete anything while the import is running. Editing or deleting any records during the migration can cause things to jam up. And potentially, cause non-reversible consequences.
If you want to refine your records, do it before or after the import.