Stabilizing port?

I am making port from a kit. The original instructions said to add the flavor pack (liqueur I am assuming along with the flavoring as it is a coffee port) at the beginning of the fermentation process. But they included an addendum saying to add it right before bottling. Do I now need to do anything to make sure that the addition of the contents will not trigger additional fermentation ? The original instructions mentioned filtering at the end of the bottling process as one way to make sure that additional fermentation did not start up after bottling. They gave no other instructions on that in the addendum.

I would follow the addendum instructions.