Do all your credits in SO, not AR...?

Seems a bit odd.  I would think if the field is read only on the inquiry screens that you could put it in multiple places. 

Maybe name the fields differently in the A/R header and S/O header?

Brainstorm:  Create a primary UDF and a secondary UDF.  Then have a UDF Script that will populate the secondary UDF from the primary.  Put the primary UDF on one panel and the secondary on the other panel.

Tom, how would you create a secondary UDF that populates the first? I am trying to create an editable field in the Invoice History Header table for "comments" and it sounds like this may be a possible solution. 

An editable field?  In invoice HISTORY header?

Can you flesh out the details of what your are trying to do?

Basically our accounting department wants to be able to have a "Comments" section which is visible/editable under customer maintenance panel. I believe this is so when they are looking at orders that don't make sense at first glance, such as "Return", "Double Payment", etc, this is easily identifiable for them. 

Again, when you own SO there is no reason to use AR Invoice Entry.  Remove permission to use AR Invoice Entry from all users to prevent accidental use, and your problem is eliminated.

If you want something editable for invoice history, within stock Sage 100, you're looking at a memo not a UDF. That won't be visible in Customer Maintenance though, only in Invoice History Inquiry.

DSD has an enhancement to allow editing posted invoice fields (but I'd be wary of users editing more than just your comment UDF).