Go to Administration > Authority types Click MARC structure of any framework, For tag 001 or 942, click subfields. Both have one subfield linked to some Koha field, but this value can't be changed. If you press Edit, 001 shows a dual edition screen and 942 only one, but neither shows an option to change Koha field. The data is sent to the template, as an scalar value in former screen, and as an CGI::scrolling_list output on editor (admin/auth_subfields_structure.pl) But template file (auth_subfields_structure.tt) does not have the code to show the corresponding pulldown. Don't know if this is a design decision, if yes some code could be removed from pl file, if no some code is needed on tt file.
This was fixed on Bug 12614