The short answer is I donno know. There are not used in the startpos that shipped with the game. They may or may not work but aren't really that important. This is what I think they do:

im is short for intro movie, om is outro after you've won or lost, in mpg format. _path_id expects a string like im_path_id:: "movie\start" without the file extension. _std_id is a subtitle delay in millisecond, it expects integer. Set _predefined_id to true if you have subtitle. _line_id are labels into startpos loc txt file. I think the outro command are not used at all, but the intro stuff may still work.

SetRegionCulture:: ID_LAND CATHOLIC_CULTURE
over write the culture of a region

SetTerrainDir:: "path to ground texture dir"

SetNumCastleMapGroups:: 4
specifies the number of castle map groups available not sure how it works exactly, but it is linked to the name of the castle maps.

set_init_agri_income_id:: 100
100 is the default, it scale the cash generate from fram up and down.