Hey there @Minna,
I definitely see why this type of adjustment on a packing slip could be desired! To be totally up front, that type of customized coding is not a skill set that I have directly and I don't want to point us in the wrong direction.
With that in mind, this is the knowledge I can provide about how to create custom packing slips including a full list of the available field replacements. I know that some of our other users may have that type of coding knowledge though! For larger format style changes like you are talking about here, my recommendation to get the best result would be to enlist the assistance of a professional coding expert.