Put it in the CS_B777-200ER_GE

In the aircraft.cfg file, you need to make sure to change these to suit the CS_B777-200ER_GE model.

As an example, here is how I added Marcelo's fictional Qantas livery to my CS_B777-200ER_GE model:

Here is the original info (included in the readme.txt file in the zip file):

[fltsim.XX]
title=CS 777-200 Captain PaintX
sim=x772
model=200
panel=
sound=
texture=qant
kb_checklists=
kb_reference=
atc_id=VH-OJB
atc_airline=QANTAS
atc_flight_number=777
atc_heavy=1
ui_manufacturer=Boeing
ui_type="777-200"
ui_variation=QANTAS
ui_typerole="Commercial Airliner"
ui_createdby="Captain Sim"
description="777-200ER VH-OJB (cn 32895/483)  Exterior Model\n777 Captain 0.2\n(c) 2011 Captain Sim www.captainsim.com"

And this is how I modified it:
[fltsim.7]
title=CS 777-200 Captain Paint7
sim=csx772_GE
model=200ER_GE
panel=
sound=
texture=qant
kb_checklists=
kb_reference=
atc_id=VH-OJB
atc_airline=QANTAS
atc_flight_number=777
atc_heavy=1
ui_manufacturer=Boeing
ui_type="777-200ER GE"
ui_variation=QANTAS
ui_typerole="Commercial Airliner"
ui_createdby="Captain Sim"
engine_type=GE90-94B
description="777-200ER GE VH-OJB (cn 32895/483)\n777 Captain 1.1\n(c) 2013 Captain Sim www.captainsim.com"

You will also need to copy the texture.cfg file from the CS_B777-200ER_GE\texture.aa folder and paste it into the Alitalia texture.XX folder.

Hope this helps