1) Create a custom map.
2) Create few custom sides.
Not sure, but you might need Zerted's 1.3 patch r117.
3) Copy any scripts you want for the stock maps. Example (myg1c_con) from C:\BF2_ModTools\assets\scripts\MYG
4) Replace the stock troops with yours in this section.
ReadDataFile("dc:SIDE\\rep.lvl",
"rep_fly_assault_dome",
"rep_inf_ep3_rifleman",
"rep_inf_ep3_rocketeer",
"rep_inf_ep3_engineer",
"rep_inf_ep3_jettrooper",
"rep_inf_ep3_sniper",
"rep_inf_ep3_officer",
"rep_fly_gunship_dome",
"rep_hover_fightertank",
"rep_hero_kiyadimundi")
And this area.
rep={
team = REP,
units = 32,
reinforcements = 150,
soldier = {"rep_inf_ep3_rifleman", 9, 25},
assault = {"rep_inf_ep3_rocketeer", 1, 4},
engineer = {"rep_inf_ep3_engineer", 1, 4},
sniper = {"rep_inf_ep3_sniper", 1, 4},
officer = {"rep_inf_ep3_officer", 1, 4},
special = {"rep_inf_ep3_jettrooper", 1, 4},
5) Open the editlocalize and change the trooper names.
6) Munge and try it. Your new era show be in the menu.
Hmmm I think thats it lol. Off the top of my head.
But if it doesnt work. Might have to back track incase I missed a step.