I told myself that I was not going to get involved with modifying aircraft files and configurations, but I was wrong ::)
Success is mine! And I am overjoyed with knowing that I have pulled it off

For those of you interested in saving disk space in your aircraft file folder and you want these 737-200 liveries then download the aircraft[s] mentioned previously in this post and follow these instructions:
1) Rename the texture folders in each downloaded aircraft to TEXTURE.1 (BA); TEXTURE.2 (AA)
**don't type what's in parenthesis in the renaming**
2) Copy these newly renamed texture files into the Boeing 737-200UAL file folder so that you have the following sub-folders within this folder: TEXTURE; TEXTURE.1; TEXTURE.2
3) Open the aircraft.cfg file and modify it with the following configuration. [this is my config and works perfectly]:
[fltsim.0]
title=Boeing 737-200 E.C.
sim=7372
model=
panel=
sound=
texture=
kb_checklists=Boeing737-400_check
kb_reference=Boeing737-400_ref
atc_type=Boeing
atc_id_enable=1
atc_id=N91SN
atc_id_color=0xffffffff
editable=0
visual_damage=1
ui_manufacturer=Boeing
ui_type=737-200
ui_variation=United airlines Friend Ship
description=United
atc_airline=United
[fltsim.1]
title=Boeing 737-200 British Airways
sim=7372
model=
panel=
sound=
texture=1
kb_checklists=Boeing737-400_check
kb_reference=Boeing737-400_ref
atc_type=Boeing
atc_id_enable=1
atc_id=N91SN
atc_id_color=0xffffffff
editable=0
visual_damage=1
ui_manufacturer=Boeing
ui_type=737-200
ui_variation=British Airways
description=British Airways
atc_airline=British
[fltsim.2]
title=Boeing 737-200 American Airlines
sim=7372
model=
panel=
sound=
texture=2
kb_checklists=Boeing737-400_check
kb_reference=Boeing737-400_ref
atc_type=Boeing
atc_id_enable=1
atc_id=N91SN
atc_id_color=0xffffffff
editable=0
visual_damage=1
ui_manufacturer=Boeing
ui_type=737-200
ui_variation=American Airlines
description=American Airlines
atc_airline=American
**DO NOT CHANGE ANYTHING BEYOND [GENERAL] in the aircraft.cfg file. FS2004 will need all that information contained there to get these birds to fly :o
My file starts with the [FLTSIM.0] and goes down the list. All you need is to copy the above and insert it into your aircraft.cfg for the BOEING 737-200 series. This modification will only work if you have the previous Boeing 737-200 downloads.
**PLEASE LET ME REMIND ALL OF YOU THAT BACKING UP YOUR FILE(S) IS NOT A BAD IDEA BEFORE ALTERING WHAT ALREADY WORKS FOR YOU**
Thanks NAV for the conk on the head in getting me to realize what was needed to achieve my goal :)
Enjoy these beautiful aircraft and happy flying!