According to this page of the plugin documentation, it is possible to override or to add a new theme by creating a
folder. While this seems to work for themes, is there any way to customise the single blocks which are used by the visual builder and are stored in the
tnp-composer folder? A requirement would be to make it update-safe, so the changes remain after the newsletter plugin is updated. Just creating a
tnp-composer folder under
extensions/ does not work.