How to remove a header bar button on a form for an extended table but retain the header bar button on the form for the parent table.
1. Go to the UI action record corresponding to the button.
2. In the Condition field of the UI action record, append a condition after the current Condition value. Make sure there's a space character between the existing value and the additional condition if you're copying/pasting.
&& current.getTableName() != 'extended_table_name'
3. Click the Update button.