After some back and forth with Acumatica support, I am told that one cannot upload a financial period outside the date range into the project transaction screen.
Support: "The program wants to default the Financial Period that corresponds to the date. This is how the system is designed. So you will need to change the dates"
The ability to upload a financial period outside the date range is needed for my clients who need to move historical costs from one project to another while retaining the original transaction date into the current period.