In a schenario where you have a dynamic footer with hundreds of rules and you have the copyright sign followed by year, you want to automatically populate that year.
So, in order for you not to manually open the footer and manually change the year, what you can do is populate that value from a field merge. Create a field merge using a datacard with email address as key.
The take the code for that field merge (simply drag the field merge in a new HTML email and you have the code) and add it to the HTML of your footer.
As you see in the image above, the value is being taked from the default value. The dacard you built will always remain empty, with no records in, so when the field merges evaluate it will always have to display the default value.
Next year, you just go and update the default value of the field merge.