I see this is an old thread, but I also would like to have an option to set the “Created By” field during import. The point is that I am importing test-plans written by different members of my team, and would like to have that ownership reflected in the test-suites.
Obviously I could just have everyone import their own test-suites, but since they are all new users of TestRail, I am taking care of this step for my whole team. This has the added benefit of giving me control over the structure and naming conventions at the time of import.
Hopefully you will consider adding this bit of functionality to the roadmap.