I want to add a new author that is not included in the accepted version to my not-yet-published paper. Can I?

You are able to add co-authors inside Confy+ during the initial submission stage and also the camera-ready stage until the deadline of said stages.

Once the deadlines have been met and/or the paper has been sent to the publisher, it is no longer possible to add co-authors.

In case that the authors can provide a signed statement explaining the contribution of the proposed new co-author it is considered, however this is done on an individual basis.