When you buy Fairfax Castle go straight to bed.

When you wake up you will have to go into these secret tunnels and kill some bandits and stuff.

After you're done at the end there is a sex change potion.

If you don't want to change but want gamer score then click yes to sex change and just after it shows the gamer score sign turn off the console.

You will have the gamerscore and your character will be the same.

It worked for me. :)