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 Getting Started page at https://www.google.com/analytics/tag-manager/get-started/.
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.
- Select Custom HTML tag.
- Name the tag.
- In the "Configure Tag" section, copy and paste in the Alexa Certify Code.
- Press Continue.
- In the "Fire on" section, select All Pages.
- Press Create Tag.
- On the upper-right hand corner, press Publish.
- Press Publish Now.
- Press Done.