Okay, thanks. But I still don't get why I just can't use pokesav to open a legit .pkm file and just change IV @ black/white. If I open a legit egg-file the PID should be fine as well I guess. And if I just change the IV @ Gen V it doesn't change anything about the PID, right? So it should work.
But if I use pokegen, I open the egg.pkm file, change IV and then leave the PID blank? Will it generate a true one after being hatched?