Hi,
Acymailing v9 is build around the new drag & drop editor. When you migrate from v5 to v9 your templates are imported as html templates that can be edited with your website's html-editor.
The available add-ons integrate nicely in the drag & drop editor and will not work with the html-editor. You can keep using the html-editor, but you need to add the tags manually and you might misss out on features.
It is recommended to rebuild your templates in the new drag & drop editor. Once you are familiar with it you will surely love all the features it offers.