Hello there, @CSAA. It's nice to have you here.

I'll be providing some details about additional columns in QuickBooks Desktop.

When your customer lists are in Hierarchical format, you can still add columns and they'll not be removed.  Let's just make sure to do it in the Customer Center.

The steps below will walk you through completing the task:

1. Go to the Customer menu.
2. Select Customer Center.
3. Right-click on any of your customers or jobs.
4. Then, select Customize Columns.
   
5. Add all the available columns you need. Click the column you want to add > Add.
6. Then, hit OK.
   

Other columns cannot be seen directly because many columns are displayed under Customer & Jobs.

To view all the columns, you need to drag the right line by placing your mouse pointer. Then, release the mouse button. Also, you can adjust the width of each column. This helps to have the desired width, so it is wide enough to contain the data of each column. 
 

I've added a sample screenshot below. As we can see, we have now a bigger space for all columns. Doing this helps us view all the data/columns we've applied.

If the same thing happens, you can run the Verify/Rebuild Utility tool. It resolves common data issues within your company file. Afterward, you'll have to restart and re-open your QuickBooks Desktop to make sure the fix applies to your book.

Let me know how it goes. I'll be around if you need further assistance with your concern. Take care and stay safe.