Update Field.JSLink using JSOM or REST

var updateJsLinkCsom = function (config) {
  var ctx = SP.ClientContext.get_current();
  var web = ctx.get_web();
  var lists = web.get_lists();
  var list = lists.getByTitle(config.listTitle)
  var fields = list.get_fields();
  var field = fields.getByInternalNameOrTitle(config.fieldTitle)
  field.set_jsLink(config.jsLink)
  field.update()
  ctx.executeQueryAsync()
};
var updateJsLinkRest = function (config) {
  SP.SOD.registerSod('sputils.js', '<your cdn endpoint>/sputils.min.js')
  SP.SOD.executeFunc('sputils.js', '', function () {
    var url = _spPageContextInfo.webAbsoluteUrl + '/_api/web/lists/getbytitle(\''
      + config.listTitle + '\')/fields/getbyinternalnameortitle(\''
      + config.fieldTitle + '\')';
    var payload = {
      '__metadata': {
        'type': 'SP.Field'
      },
      'JSLink': config.jsLink
    };
    var config = {
      'headers': {
        'X-HTTP-Method': 'MERGE'
      }
    };
    sputils.rest.post(url, payload, config);
  });
};
var config = {
  listTitle: '<your list title>',
  fieldTitle: '<your field title>',
  jsLink: '~site/<your jslink>'
};
updateJsLinkCsom(config);
updateJsLinkRest(config);