Hi Raphael,
If you have a text file with the IPTC Subject Codes, then you can Import this into the IPTC dialog, IPTC Subject Code's popup list. The text file should have one code per line. Go to the IPTC dialog and click the down arrow at the right end of the IPTC Subject Code field. Click the Edit IPTC Subject Code option at the top of the list. In the Edit IPTC List dialog, click the Import button at the bottom and then locate your text file. Double click the file should open it and now you should see the 8 digit codes in the center field. Click the OK button to save the changes. Enabling the Autocomplete option to only use a field's popup list might help save some time when entering a code in this field.
Best regards,
--Bob