Add custom messages onto Parcelforce labels

Parcel force has the ability to have custom messages on the label, this is to allow customers to add delivery instruction for example leave in porch or leave with neighbour. Currently although Parcelforce allows this Shipstation have not integrated this to be available, for us we are having to manually add the delivery messages on the label which is very time consuming. Would it be possible to please add the custom message functionality to the parcelforce labels