Quote - I want to add say six or more items of props and objects at once to the library as a .pp2 file and not as a scene (.pz3 file).

Select any prop, click the "+" button to save to the library, then when the dialog asking for a name appears, click on the "Select Subset" button, and click next to each prop that you want to include in the file so that a cross appears next to it, click OK, type the name for the set and click OK.