Let's start with the basics. How to import a headmorph into your Mass Effect 3 save game.
Headmorphs let you swap appearances between save games and you'll recognize them by the file extension .me3headmorph.
Download the latest version of Gibbed's ME3 Savegame Editor.
Open up Gibbed's save editor and you will see a row of buttons and 2 rows of tabs.
1. Hit "Open" and load the save game you want to edit.
2. Navigate to the "Appearance" tab in the bottom row of tabs, next to "Basic".
3. There will be 2 drop-down menus: "Head Morph" and "Presets"
Click "Head Morph" and you will see two options, click "Import from File..."
A navigation window will open for you to find your desired head morph.
In the case of my customized Femshep it will be "ELE_defem_brunette.me3headmorph"
or just "ELE_defem_brunette" if you don't have file extensions visible.
Select it and hit "Open"
Now at the top of Gibbed, hit "Save" and either create a new save file or overwrite your existing one. It's always a good idea to make a new one if your not sure of the results of your tweaks.
If you load up your save in Mass Effect 3, your Shepard should have new face.