Markoz, I believe my doubt is solved.

Remark about this "How to": CS do not support neither modifications of the original package nor the issues caused by the modifications. Do it at your own risk.

How to do, step by step:

1) Open Windows Explorer > Program Files > Microsoft Games > SimObjects > Airplanes > CS_B767-300

2) Now, click one time on "Aircraft.cfg"

3) Click in "Files" (upper tool bar)

4) Click in "Edit"

A new window will open (notepad)

There is a list of all CS planes, numbered from 0 up to 13. The configuration of each model appears as below (the first one [fltsim.0]
is Aeroflot model):

[fltsim.0]
title=CS 767-300 Captain Paint0
sim=B767-300GE
model=ge5
panel=
sound=GE
texture=aeroflot
kb_checklists=
kb_reference=
atc_id=N764A
atc_airline=
atc_flight_number=
atc_heavy=0
atc_parking_types=
ui_manufacturer="Boeing"
ui_typerole="Commercial Airliner"
ui_createdby="Captain Sim"
ui_type="767-300 GE"
ui_variation="Aeroflot"
description="767-300 Base Pack v1.4\n(c) 2009 Captain Sim www.captainsim.com"
ui_wglts=0

5) Go to 11th line (atc_airline=)

6) Add Aeroflot after the equal sign. So, the new 11th line will be: atc_airline=Aeroflot

7) Save the file

8) Start FSX, load a presaved flight, change the aircraft to "CS Aeroflot", choose a flight number (551) in "details", click "OK" and "Fly Now".

Now all ATC comm will be adressed, for example, to "Aeroflot 551", instead of default airplane's alphanumeric registration (Boeing N-764A).

Sources of Airlines Call Signs:

http://en.wikipedia.org/wiki/Airline_call_sign#Call_signs

http://www.atcmonitor.com/callsigns.html

http://www.airlinecodes.co.uk/airlcodesearch.asp