Thank you for the answer Kwok.
But what do you do if you want to modify an existing .csf file? Can you convert it back to a text file or do you need the original text file??
Anyway it seems to me that modifying will be more complicated compared to SE IV.
You cannot edit the .csf files directly. You'd need to make your changes in the base text files and re-make the .csf file.
Modding the data files themselves is probably a bit easier since it's one entry per item. Only the intelligence and events file use scripts of the non-AI files.