Uses Cascade CMS REST API to iterate over XHTML/SD Blocks which subscribe to a specific Data Definition and adds a tag to each one.

tag_blocks_subscribing_to_dd.js

// To install module, run: `npm i node-fetch`
const fetch = require("node-fetch");

const AUTHENTICATION = {username: '...', password: '...'};
const REST_API_URL = 'https://CASCADE_URL/api/v1/';

const SITE_NAME = 'www.example.com';
const DATA_DEFINITION_NAME = 'foo';
const TAG_TO_PUSH = 'bar';

function postData(restEndpoint, data = {}) {
    data.authentication = AUTHENTICATION;

    return fetch(REST_API_URL + restEndpoint, {
        method: "POST",
        headers: {"Content-Type": "application/json; charset=utf-8"},
        body: JSON.stringify(data),
    })
    .then(response => response.json());
}

postData('listSubscribers/structureddatadefinition/'+SITE_NAME+'/'+DATA_DEFINITION_NAME)
  .then(data => {
    if (!data.subscribers.length) {
      console.log('No subscribers found.');
      return;
    }

    data.subscribers.forEach(subscriber => {
      if (subscriber.type !== 'block_XHTML_DATADEFINITION') {
        console.log('Subscriber was not an XHTML/SD Block, skipping.');
        return;
      }

      console.log('Reading Block with ID: ', subscriber.id);
      postData('read/block/' + subscriber.id)
        .then(readResponse => {
          let blockData = readResponse.asset.xhtmlDataDefinitionBlock;

          console.log('Updating Block tags');
          blockData.tags.push({name: TAG_TO_PUSH});

          postData('edit/block/' + subscriber.id, {
              asset: {
                xhtmlDataDefinitionBlock: blockData
              }
            })
            .then(editResponse => console.log('Updated Block tags'))
            .catch(error => console.error(error));
        })
        .catch(error => console.error(error));
    });
  })
  .catch(error => console.error(error));