No. But if you modify the view options in layout set up to show the header, you can put this field in the header and it will show the ID of the record that you are currently editing. That might allow you to place this copy of the field on the far right edge of your view.
400 columns is an extremely large number of fields in one table. (And I'd be amazed if you can see all 400 at the same time given the limits of a table view.) It suggests that you might be able to make major improvements in your data model by employing related tables to reduce the number of fields in one record.
That is a good idea and has been implemented. However, I have many related tables, but the sum total of the fields in each table is around 400, therefore, these all show up in Table View. When I scroll to the right in table view to edit field 256, I cannot see the first column, nor if I put it in the header (unless copy/paste the field into the header at different horizontal locations)
This sounds like an interface design that could benefit greatly from a list view rather than a table view.
However, I have many related tables
But in table view, you can only see the data from one related record--the first related record, since there is no way to use a portal to see multiple related records. From a functional point of view, that's the same has having one large table with all of the fields from your related table incorporated as fields in the same table. And that brings me back to the observation that "400 columns" is an extremely large number to have in one table (or the functional equivalent of one table).