Much like my other idea logged for exporting Bank Details as part of the supplier export routine - https://www.sagecity.com/gb/sage-200cloud-uk/i/sage-200cloud-uk-ideas/for-the-suppliers-export-option-to-export-supplier-bank-details I am logging this because when you export customers or suppliers it doesnt export the default contact records.
Like the above wish, if creating new companies and the customer and supplier base is similar or the same, then you should be able to export details with a default contact - of course you cannot import multiple contacts but you can import one (https://www.sagecity.com/gb/sage-200cloud-uk/i/sage-200cloud-uk-ideas/to-be-able-to-import-multiple-contacts-on-pl-sl-accounts) - R&D say the contact details cannot be overwritten on an import "over the top" - thats fine but please export the contact records for new imports.