You'd need to first re-number all the customers and their addresses, and then renumber the address records for the customers (there's a two-way relationship to maintain). And then you need to renumber all the customer ids in all the orders to use the new numbers. And then you need to renumber all the orders. And in all those cases there are multiple tables having multiple IDs that need maintaining all the way through. And then copy all those records over.

I'm extremely reluctant to just "hand over a list of tables" because I'm scared that you'll just run off and break everything. To be honest, if someone is asking the questions you're asking, then you're definitely not the person who should be tackling this exercise. Nevertheless, the list of tables is here: http://www.zen-cart.com/wiki/index.p...atabase_Schema