I've added the infrastructure selection function (https://github.com/simutrans/tutorial_multipak/blob/914f4c7c66047a700a546c085c425293dba2c9b5/class/class_basic_chapter.nut#L3583) (bridge, tunnel, way, catenary) from the script AI and extended it for the postal service (station, extension).
This allows object selection to be automated instead of having to define it manually for each package set.
Vehicles, however, should still be defined manually.
object search function (https://github.com/simutrans/tutorial_multipak/blob/914f4c7c66047a700a546c085c425293dba2c9b5/class/class_basic_chapter.nut#L3583)