Maybe it's possible to make the import numerous scenes to a pack at the same time?
That could be done.
And maybe there is a way to make saving easier. Like in a huge twogirls pack only the changed girls would be saved? Because from the process I see that girls without changes are saved too. So maybe something like in windows when overwritting? To be able to skip the girls that didnt get any changes?
Can't be done. The format is one continuous (serial) stream, so if you add only one byte of data in the first girl all the following girl infos and movie data will be offset by that one byte. All the entry points to the movies have to be calculated, which is done while saving.
Remember I told you to split your packs into managable sizes of around 1 to 2 GiB of data? Also consider a SSD for your data, which will significantly improve your system's performance. Current prices are at 70 euros for 256 GiB.
And one more thing. When the girl is already in the TempGirl folder the editor gives error that says "the file already exists".
So can you make it to just use that file instead of trying to create it once again?
This is in fact a safety feature. Since the program doesn't know if it's exactly the same file or only a file by the same name, it aborts the current operation.