First of all, thank you!

I transferred my game to my new PC using an external harddrive, then copied it all to my new internal HD so it's faster. Works like a charm.
Now I'm trying to add Seasons to it. Could you explain how that works in more detail? I Installed it with my local Sims 3 game on my old PC, then moved the directory to the App folder on my new PC, properly named. I also tried to change the REG files, but I'm not sure I did it right. There is one for Seasons already, and the latest EP I have installed is Supernatural. So I changed the Supernatural REG file the way you described. Or am I supposed to do something with the Seasons REG file?
Whatever I did wrong, it doesn't work.
Weirdly, I also installed Pets yesterday just by copying the directory into the /App folder, no REG file changing, and it works.

What did I do wrong?