When you are in the All tab or the Record window, you can press Delete to delete a field (or fields). A natural progression of this is to allow the Ins key to insert a field.
It won't be possible to know which field to add, so FH will have to display the context menu available with a right click but without the editing options of Copy/Paste (and Delete which for some reason is missing from the context menu). The user can then add fields using the keyboard only, selecting the appropriate field from the context menu with cursor keys, or even the first letter of the field name.
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