On the BF Editor there is a way to make 4 factions / teams / flags.

Anyone have a working editor?
We can make a mod ex to work.

Copy all the animations and files for skins etc for german and british to the Japanese et and US folder.
Make all the names Japanese and US

Mod the GameLogicInit.con file and make this changes.

rem *** Put non level specific initializations here ***
This say to mod faction mod etc we are adding jap and US faction .

gameLogic.setTeamName 1 "National"
gameLogic.setTeamName 2 "British"
gameLogic.setTeamName 1 "Imperial"
gameLogic.setTeamName 2 "US"

gameLogic.setTeamLanguage 1 "Russian"
gameLogic.setTeamLanguage 2 "English"
gameLogic.setTeamLanguage 1 "Russian"
gameLogic.setTeamLanguage 2 "English"

gameLogic.setTeamFlag 0 "flag_neutral"
gameLogic.setTeamFlag 1 "flag_NA"
gameLogic.setTeamFlag 2 "flag_RA"
gameLogic.setTeamFlag 3 "flag_neutral"
gameLogic.setTeamFlag 4 "flag_IA"
gameLogic.setTeamFlag 5 "flag_US"
You need to mod a map for this / add a flag for US and Imperial teams / Japanese

gameLogic.setKit 1 0 "NA_Commando_kit" "german_male_commando" "german_male_commando"
gameLogic.setKit 2 0 "RA_Commando_kit" "british_male_commando" "british_male_commando"
gameLogic.setKit 3 0 "IA_Commando_kit" "IA_male_commando" "IA_male_commando"
gameLogic.setKit 4 0 "US_Commando_kit" "US_male_commando" "US_male_commando"

You need to make new Commando
gameLogic.setKit 1 1 "NA_Soldier_kit" "german_male_soldier" "german_male_soldier"
gameLogic.setKit 2 1 "RA_Soldier_kit" "british_male_soldier" "british_male_soldier"
gameLogic.setKit 3 1 "IA_Soldier_kit" "german_male_soldier" "german_male_soldier"
gameLogic.setKit 4 1 "US_Soldier_kit" "british_male_soldier" "british_male_soldier"

gameLogic.setKit 1 2 "NA_Gunner_kit" "german_male_gunner" "german_male_gunner"
gameLogic.setKit 2 2 "RA_Gunner_kit" "british_male_gunner" "british_male_gunner"
gameLogic.setKit 3 2 "IA_Gunner_kit" "german_male_gunner" "german_male_gunner"
gameLogic.setKit 4 2 "US_Gunner_kit" "british_male_gunner" "british_male_gunner"

FEMALES?
rem gameLogic.setKit 1 3 "NAF_Commando_kit" "german_female_commando" "german_female_commando"
rem gameLogic.setKit 2 3 "RAF_Commando_kit" "british_female_commando" "british_female_commando"

rem gameLogic.setKit 1 4 "NAF_Soldier_kit" "german_female_soldier" "german_female_soldier"
rem gameLogic.setKit 2 4 "RAF_Soldier_kit" "british_female_soldier" "british_female_soldier"

rem gameLogic.setKit 1 5 "NAF_Gunner_kit" "german_female_gunner" "german_female_gunner"
rem gameLogic.setKit 2 5 "RAF_Gunner_kit" "british_female_gunner" "british_female_gunner"

rem *** Load multiplayer free camera here
run Common/FreeCamera/Object.con

gameLogic.setDefaultNumberOfTickets 1 250
gameLogic.setDefaultNumberOfTickets 2 250

gameLogic.enableVoHelp 1
gameLogic.supplyDropHeight 50
gameLogic.supplyDropNumSecsToLive 300

run mods/bfheroes/BandwidthOptimizationSettings.con