Hey there, @sanchezelectric.
I hope you're enjoying this beautiful day so far.
I recommend to export your customer list to an Excel worksheet and make your changes there and then import the list back into the company file. You can also use our Add/Edit multiple list entries feature in the program. Below I've included the steps to export and import the list into QuickBooks.
1. First, you'll want to create a back up of the company file.
2. Once your back up has been created, Open the Customer Center.
3. At the top, click the Excel drop-down and choose Export Customer List.

4. Choose Create new worksheet. (Yours will not be grayed out as mine is if you have Excel installed on your PC).
5. Hit Export once you're ready to export.

To import the data back in the file after the changes have been made:
1. Open the File menu.
2. Choose Utilities then Import.
3. Click Excel Files.

4. Here is the option if you choose to use our Add/Edit Multiple List Entries feature. (Please note: When using this feature you can copy and paste the data straight from Excel to QuickBooks without having to go through the import process. Check out, Add and edit multiple customers, vendors, and items for more details).
5. To continue to go through the import process, select No.

6. Pick Customers from the list.

7. Select Yes to the message that appears to continue.

8. Locate your saved Excel worksheet by hitting Browse.
9. Lastly, click Add my Data Now.

You can check out these helpful articles for more detailed information about importing and exporting in QuickBooks.
Please don't hesitate to reach back out anytime if you have further questions or concerns. I'll be here to help you every step of the way. You can always reach out to us here in the Community anytime you need assistance. Take care and have a great weekend ahead!