How do I "remap" my Chart of Accounts? Should I create a dummy company as a safeguard to avoid the risk of corrupting my original set of books?

Congratulations on the success of your start-up, rpv! It's great to hear you're taking a thoughtful approach to remapping your Chart of Accounts (COA). 

Using a dummy company is indeed a smart strategy to safeguard your existing data. You’re on the right track of exporting all transactions to a CSV file, remapping accounts in Excel, and importing the updated transactions into a test company, as this is an ideal way to handle this process without risking your current records. 

To learn more about the data that can be exported and imported in QuickBooks, refer to these articles:

• Export your QuickBooks Online Data
• Common questions about importing data to QuickBooks Online

Please also note QBO allows you to safely rename existing accounts or merge redundant ones directly, which helps in mapping and reclassifying transactions without the need for a full re-import process.

It would also be best to consult your accountant for accurate bookkeeping and account management. 

If you have further questions regarding your concern, feel free to reply below.