Yes, you can! First you need to make sure that Google Tag Manager is installed on your site. For information on how to install GTM, check out the Setup and Installation page at GTM Setup and installation.
After you've got Google Tag Manager setup, you can add the Alexa Certify Code to it with these steps:
- Go to the container for your GTM account.
- Click New Tag.
- Click Tag Configuration and select Custom HTML.
- In the HTML section, copy and paste in the Alexa Certify Code.
- Click Triggering and select All Pages.
- Name the tag.
- Press Save.
- On the upper-right hand corner, press Submit.
- Add a description if you'd like, or go on to step 10.
- Press Publish.