Yes, if the product code matches an existing one then the import process would treat that as an update to the existing product.

Thank you Darron. These are new products so will be all new product codes. So as long as the product codes are different the old ones should remain unchanged is that correct?

Correct. The process will be additive. If you are in any doubt then you can always test it using the demo or practice data. I'd also recommend taking a backup of your data first so you can always restore it things did not work as you expected (not that I think this will be the case here of course)

Brilliant thanks for your answer. I am going to have a play in the test system that's a great idea.