For custom fields, Hubspot's API will only pull in ID numbers for each field. Unfortunately, there is no endpoint that will let us pull in the custom field IDs and map them to their field.
As a workaround, we suggest isolating them and keeping track in a Google Spreadsheet of the IDs and the assigned codes. You can then group by ID or map them better.
Questions? Chat in on the site and we'll be happy to help.