Hello, Mjg86.
I appreciate you for reaching out to us about the multi-currency feature. Allow me to chime in and share information about how multi-currency works in QuickBooks Online.
If Multi-currency is already turned on, take note that QuickBooks doesn't allow you to change the home currency. This is to avoid messing up the account, especially when adjusting the sales tax. Yes, I agreed that you can set it up with USD as home currency and then import the data if this is a new company.
You can check this article for more details: Learn about Multicurrency in QuickBooks Online.
Additionally, I've included this article to help you assign a foreign currency to a customer in QuickBooks Online,
Let me know how this goes and leave a reply below if you need further assistance managing currency. I'm always here to help. Have a good one.