Quickbooks Jobs

You could change existing customers to be Jobs under a parent customer but that moves all historical data.  Instead just add Job as needed under any parent customer level. You can enter a duplicate name for the sub-customer compared to that pre-existing customer at a parent level because it bypasses the prohibition on duplicate names purely due to the fact that the full name of the Job includes the parent level(s)

This means you also can have the individual name of a Job under multiple customers with no problem

If I wanted to go ahead and change it historically as well, what are the exact steps to move a customer to a job under the parent customer?

It is not as easy as I first thought. You can merge parent level customers into an existing customer or into a new parent customer, and you can move and merge jobs once they are changed to a parent level by renaming but there is no way during edit to change a customer to a job.

Despite this issue with subname s , when viewing your customer list in hierarchal voew you CAN drag a customer with subnames into another customer that also has subnames

https://quickbooks.intuit.com/learn-support/en-us/reports-and-accounting/can-two-different-customers...