.. to transfer my character from one save file to another.

I like the looks of my old character better then the new one.

They are the same race and gender.

you mean like from Oblivion to Skyrim? no not possible.

No, no I mean Skyrim.

Don't think it's possible. But I could be wrong.

However, why not keep playing your first character? If you like that one better.

If you're playing on PC. Anything is possible with enough effort.

Console? No.

I waked Dark Brotherhood and then decided to join them, and completed Thief Guild but what to get best stats for Nightingale Armor. Among other things....

If you are on the PC, there will be tools that you can use to import a face from one save file to the other. At least there is for earlier games. However, I don't know if the current engine will support that feature from a third party tool. Check the mods section for Wrye Bash for Skyrim and see how that is.

Also, this maybe too late, but you could load a save that you made just after or during the intro cell and start over from there.

Interesting I try that tool. Thanks CCNA.