Thank you, Gargabee.
PS: it appears that the file is located under All users directory (or whatever it called under Windows). I.e. I've found it here:
WINEPREFIX/drive_c/users/Public/Application Data/Ironclad Games/Sins of a Solar Empire/License/rebellion.bin
So under Windows it could be here:
WINDRIVE/Documents and settings/All users/Application Data/Ironclad Games/Sins of a Solar Empire/License/rebellion.bin
Maybe it's because the game was installed through Steam.