Updates one field option by its field option id. Only the properties present in the request are changed, with one exception: every update rewrites the label to match the option's value unless the update also changes the label to new text (the campaign preferred-language field is the only exception). Sending the current label back does not preserve it, so a label that differs from its value is lost on any update that leaves the label unchanged. Renaming an option does not update contacts: a contact whose saved value is the old text keeps it until the contact is edited. 404 if no option has this id.