[Count von Phoib]

First of all, a huge thanks to Lauren, who gave the necessary Position code here.

Adding starting units in RA3 is easier then in previous games, and you are no longer confined to 10 units max.

First of all, open up SageXML\System\PlayerTemplates.xml

Find the code for the faction you want to give starting units.

CODE

<PlayerTemplate
id="Allies"
Side="Allies"
Type="PLAYABLE"
StartingBuilding="AlliedConstructionYard"
ScriptedHuntTactic="ScriptedHuntTactic"
DisplayNameToken="INI:FactionAllies"
FactionIconImageName="GameSetup_flag_Allied"
UnattachedMpBeaconTemplate="MultiplayerBeacon"
AttachedMpBeaconTemplate="MultiplayerBeaconAttached"
MaxMpBeacons="=$PLAYER_MAX_MP_BEACONS"
LoadScreenMusic="TEMP_RAM_Music360_LoadScreen"
SkirmishMPVictoryMusic=""
SkirmishMPDefeatMusic=""
FactionDataPathMusicEvent="SetPlayerAllied"
MatchVictoryPathMusicEvent="S_EndMissionWin"
MatchDefeatPathMusicEvent="S_EndMissionLose"
SpellBookSP="PlayerSpellBook"
SpellBookMP="PlayerSpellBook"
NumberOfResourceAccounts="1"
ParachuteOCL="OCL_AlliedParachute"
DefaultTech="PlayerTech_Allied"
PlayerTechUpgradeBinding="PlayerTechUpgradeBinding_Allied"
TechRankPointsPerSecond="1"
InitialTechPoints="1"
PowerOutageTurnsOffRadar="false">
<RedAlertTemplate>BaseRedAlert</RedAlertTemplate>
<PreferredColor R="50" G="75" B="200"/>
<PreferredCampaignRadarColor R="50" G="75" B="200"/>
<InitialUpgrade>Upgrade_AlliesFaction</InitialUpgrade>
<StartingMoney Account="=$ACCOUNT_ORE" Amount="10000"/>
<MoneyCap Account="=$ACCOUNT_ORE" Amount="999999"/>
<AIBeaconSettings
BeaconType="Assault"
UnattachedTemplate="AIAssaultBeacon"
AttachedTemplate="AIAssaultBeaconAttached"/>
<AIBeaconSettings
BeaconType="HoldObject"
AttachedTemplate="AIHoldBeaconAttached"/>
<AIBeaconSettings
BeaconType="HoldPosition"
UnattachedTemplate="AIHoldBeacon"/>
<TechRank>PlayerTechRank_Rank1</TechRank>
<TechRank>PlayerTechRank_Rank2</TechRank>
<TechRank>PlayerTechRank_Rank3</TechRank>
<TechRank>PlayerTechRank_Rank4</TechRank>
<TechRank>PlayerTechRank_Rank5</TechRank>
<TechRank>PlayerTechRank_Rank6</TechRank>
<TechRank>PlayerTechRank_Rank7</TechRank>
<TechRank>PlayerTechRank_Rank8</TechRank>
<TechRank>PlayerTechRank_Rank9</TechRank>
<TechRank>PlayerTechRank_Rank10</TechRank>
<TechProductionBonuses
RequiredTech="PlayerTech_ProductionBonus_Allies"
HarvesterBonus="25%"
HarvesterBonusAllies="5%"
/>
</PlayerTemplate>

(An example of faction code) and locate the following two lines

CODE

        <InitialUpgrade>Upgrade_AlliesFaction< /InitialUpgrade>
        <StartingMoney Account="=$ACCOUNT_ORE"        Amount="10000" />

In between, add the following code:

CODE

        <StartingUnitInfo>   
             <Object>StartingObject</Object>  
              <Position  
               x="11.0"  
               y="11.0"  
               z="0.0" />
        </StartingUnitInfo>

Where StartingObject is the object you want to start with.

Two notes:

1. The position fields are ignored. The game will place the units around the Conyard in a predetermined matter.
2. This has been stress tested up to 40 units. Higher is certainly possible, but do mind, you will start with a screen full of units.

[Count von Phoib]

Example of code where the Allies start with 1 Athena Cannon:

CODE

    <PlayerTemplate
         id="Allies"
        Side="Allies"
        Type="PLAYABLE"
         StartingBuilding="AlliedConstructionYard"
         ScriptedHuntTactic="ScriptedHuntTactic"
         DisplayNameToken="INI:FactionAllies"
         FactionIconImageName="GameSetup_flag_Allied"
         UnattachedMpBeaconTemplate="MultiplayerBeacon"
         AttachedMpBeaconTemplate="MultiplayerBeaconAttached"
         MaxMpBeacons="=$PLAYER_MAX_MP_BEACONS"
         LoadScreenMusic="TEMP_RAM_Music360_LoadScreen"
         SkirmishMPVictoryMusic=""
        SkirmishMPDefeatMusic=" "
        FactionDataPathMusicEvent="SetPlayerAllied"
        MatchVictoryPathMusicEvent="S_EndMissionWin"
        MatchDefeatPathMusicEvent="S_EndMissionLose"
        SpellBookSP="PlayerSpellBook"
         SpellBookMP="PlayerSpellBook"
         NumberOfResourceAccounts="1"
         ParachuteOCL="OCL_AlliedParachute"
        DefaultTech=" PlayerTech_Allied"
        PlayerTechUpgradeBinding=" PlayerTechUpgradeBinding_Allied"
        TechRankPointsPerSecond=" 1"
        InitialTechPoints="1"
         PowerOutageTurnsOffRadar="false">
         <RedAlertTemplate>BaseRedAlert</RedAlertTemplate>
         <PreferredColor R="50" G="75" B="200"/>
        <PreferredCampaignRadarColor R="50" G="75" B="200"/>
        <InitialUpgrade>Upgrade_AlliesFaction< /InitialUpgrade>
        <StartingUnitInfo>   
                 <Object>AlliedAntiStructureVehicle</Object>  
                  <Position  
                   x="10.0"  
                   y="10.0"  
                    z="0.0" />  
         </StartingUnitInfo>
        <StartingMoney Account="=$ACCOUNT_ORE" Amount="10000"/>
        <MoneyCap Account="=$ACCOUNT_ORE" Amount="999999"/>
        <AIBeaconSettings
        BeaconType="Assault"
         UnattachedTemplate="AIAssaultBeacon"
         AttachedTemplate="AIAssaultBeaconAttached"/>
         <AIBeaconSettings
        BeaconType="HoldObject"
        AttachedTemplate="AIHoldBeaconAttached"/>
        <AIBeaconSettings
         BeaconType="HoldPosition"
         UnattachedTemplate="AIHoldBeacon"/>
        < TechRank>PlayerTechRank_Rank1</TechRank>
         <TechRank>PlayerTechRank_Rank2</TechRank>
         <TechRank>PlayerTechRank_Rank3</TechRank>
         <TechRank>PlayerTechRank_Rank4</TechRank>
         <TechRank>PlayerTechRank_Rank5</TechRank>
         <TechRank>PlayerTechRank_Rank6</TechRank>
         <TechRank>PlayerTechRank_Rank7</TechRank>
         <TechRank>PlayerTechRank_Rank8</TechRank>
         <TechRank>PlayerTechRank_Rank9</TechRank>
        <TechRank>PlayerTechRank_Rank10</TechRank>
        <TechProductionBonuses
         RequiredTech="PlayerTech_ProductionBonus_Allies"
         HarvesterBonus="25%"
         HarvesterBonusAllies="5%"
        />
     </PlayerTemplate>

[Count von Phoib]

And as small addendum:

Bibber posted about it earlier, but since the search function of the EA forums sucks, I didn't know about it. Still, kudos to him.