I would like to show a specific advert to the user when one my of tags is loaded with a specific rule. I'm planning to show the advert using an image tag or with a simple div. Is there a best practice way to do this with Tealium? Is it acceptable to insert html using a custom template on the tag?
So you could do this with a tag, however, the content modification extension might be easier for you to achieve the outcome you are after.