Is it possible to use different DS_MAPPATH/DS_MAPSIZE/DS_MAXWRITEHEAPS
settings for different DataStage Projects/Jobs or is this more a environment variable for the DataStage instance?
Should be OK to do, so long as you set the environment variables after dsenv has been executed. Also, you must do this for each process; remember that active stages run in separate processes from their jobs. You could, for example, use the UniVerse command ENV.