This will automate setting custom parameters for your adwords tracking template at the campaign and adgroup level.

AdwordsScript.js

// Sample Tracking Template
// {lpurl}?utm_medium=adwords&utm_campaign={_campaign}&utm_source={_adgroup}&utm_term={keyword}
// This script will set custom parameters {_campaign} and {_adgroup}  at the campaign and creative level respectively.

function main() {
  
  ///// Update Campaigns
  // get all campaigns
  var campaignSelector = AdsApp
  .campaigns()
  .withCondition("Status NOT_IN ['REMOVED']")
  .withCondition('CampaignStatus != REMOVED');

  // Update those campaigns with the new tracking template
  // {_campaign = <name of campaign>}
  update_campaign_parameters(campaignSelector);
  
  
  ///// Update AdGroups
  // Get All Adgroups  
  var adgroupSelector = AdsApp
  .adGroups()
  .withCondition("Status NOT_IN ['REMOVED']")
  .withCondition('CampaignStatus != REMOVED');
  
  // Update the adgroups with the new tracking template
  // {_adgroup = <name of adgroup>}
  update_adgroup_parameters(adgroupSelector);
}


function update_campaign_parameters(campaignSelector) {
  // loop through campaigns and update the tracking template
  var iterator = campaignSelector.get();
  while (iterator.hasNext()) {
    var campaign = iterator.next();     
    var campaign_name = campaign.getName();

    param_value = format_parameter_value(campaign_name);          
    new_custom_parameters = get_new_custom_parameters(campaign, 'campaign', param_value);

    // Update the campaign and set the custom parameters     
    Logger.log("Campaign: " + campaign_name + "|" + new_custom_parameters['campaign']);
    campaign.urls().setCustomParameters(new_custom_parameters);
  }
}

function update_adgroup_parameters(adgroupSelector) {
  // loop through campaigns and update the tracking template
  var iterator = adgroupSelector.get();
  while (iterator.hasNext()) {
    var adgroup = iterator.next();     
    var adgroup_name = adgroup.getName();

    param_value = format_parameter_value(adgroup_name);          
    new_custom_parameters = get_new_custom_parameters(adgroup, 'adgroup', param_value);

    // Update the adgroup and set the custom parameters     
    Logger.log("Adgroup: " + adgroup_name + "|" + new_custom_parameters['adgroup']);
    adgroup.urls().setCustomParameters(new_custom_parameters);
  }
}





// // replace spaces with underscores, remove all characters that is not a number or letter.
// replace spaces with underscores (only)
function format_parameter_value(adwords_name) {  
  //return adwords_name.replace(/[^a-z_\d ]+/ig,'').toLowerCase().replace(/  /g, ' ').replace(/ /g, '_').substr(0, 50);
  return adwords_name.replace(/\s/g,'_')
}

// Whether it be an adgroup, ad, or campaign - bget the new tracking parameter.
function get_new_custom_parameters(adwords_object, parameter_name, parameter_value) {              
  var custom_parameters = adwords_object.urls().getCustomParameters();
  var new_custom_parameters = {};
  if (custom_parameters == null) {
    new_custom_parameters[parameter_name] = parameter_value;
  } else {
    if (custom_parameters[parameter_name]) {
      // update existing value
      custom_parameters[parameter_name] = parameter_value;
    } else {
      // has parameters, but not the adwords parameter. Make sure we have room for one more parameter.         
      var num = Object.keys(custom_parameters).length;
      if (num < 3) {
        custom_parameters[parameter_name] = parameter_value;
      }         
    }       
    new_custom_parameters = custom_parameters;
  }
  
  return new_custom_parameters;
}