Being able to see the Additional Info fields on the main customer detail screen is an excellent idea, @DenisB87!
While this isn't an option in QuickBooks, I have another workaround you can consider performing. You can add the identifier value on the Notes field instead. This way, you'll see the said info on the main customer window.
I've got the needed steps to ensure your success. Here's how:
- Go to the Customers menu, and then choose Customer Center.
- Select a customer, and then navigate through the Notes tab.
- Choose Add New from the Manage Notes drop-down.
- Add the identifier value, and then click OK when you're ready.

Also, you can run the Transaction List by Customer report, and then customize it to see the transactions linked to a specific customer. To do that, go to the Reports menu and then select the said report from the Customers & Receivables section.
Lastly, I recommend visiting our Firm of the Future site to get you in the loop about the latest news and product enhancements.
I'm always around to help if you have some questions about managing your customer info in QuickBooks. Take care.