Is it possible to create a Supplier from an existing Customer using REST API?

Summary:

Is it possible to create a Supplier from an existing Customer using REST API?

Content (please ensure you mask any confidential information):

We are using the REST API to create Suppliers and Customers.

Sometimes we have the need to make an existing supplier, become a customer, and the other way, to make an existing customer, become a supplier.

From supplier to customer all works well. When trying to go from customer to supplier also, it duplicates the organization.

Is there a way to do this using the REST API? I read here on the forum some people advising to create the supplier using the "Import" feature, but my question is, can we do it with the API, or the spreadsheet feature is the only option?