Hello Luke55,

I’d like to give you some insight on this.

It is absolutely possible to export your customer information and import it back into QuickBooks Online. However, imported lists will not replace the old information but will add up to the existing lists on file. Having said that, you will need to edit the customer information and merge them.

Therefore, I suggest updating your customer information in QuickBooks Online. This way, it will be less complicated for you.

Here’s how you edit the customer information in QuickBooks Online:

1. Click the Sales tab on the left panel and select Customers sub-tab.
2. Select a customer.
3. Click Edit.
4. Enter your changes as needed. 
5. Click Save.

Let me know if you need more help. I’ll be a few clicks away.