Dos Registry editor

I’ve had a win 98 machine bought to me that wont run, neumerous reg files corrupted. My idea is to use pcrestor but it needs the origonal CD key to complete the owner doesn’t have it anymore and my copy of Win 98se won’t get passed the CD key. any ideas, I’m planning editing the registry to change the CD key to my copy so that I can run pc restor. any ideas?