Moving to New Legal Employer in a Flex Credits Program

Summary: I have a client that is moving their employees from one legal employer to a new legal employer and these employees are enrolled in a flex credit program. I thought it would be as easy as creating the flex credit configuration for the new legal employer under the same flex credit shell plan. But when I try and add the rates under Credit Pools > Spending options, I get the following error message:

You can't select a rate as a spending option more than once. (BEN-991131) The rate that you selected already exists as a spending option.

This rate does already exist under the original legal employer. I then tried to end date the same rate in spending options for the original legal employer, but I get the following error message: