Hi there, @BLSafe.

It's good to have you here in the Community. I'd like to help share some information about creating a sub-customer in QuickBooks Online. 

Yes, you are correct. If you're going to create a whole new sub-customers the previous transactions that you've created will not sync to the new one. In your, case I'd suggest continuing editing the customer's details to keep your invoices intact. 

Here are some great articles that you can check out about dealing with customers and sub-customers in QuickBooks Online for your future reference:

• How to add a customer or sub-customer.
• How to add, delete, merge, and restore a customer.
• How to convert existing sub-customers and transactions into a project.

This should get you moving today, @BLSafe.

Please reach back out to me if you have any other questions with creating new sub-customers in QuickBooks Online or anything about QuickBooks. Helping you will always be my pleasure. Thanks for dropping by and wishing you all the best in everything that you do.