To replace, use OpenIV to navigate to:

MODS\ X64E\ LEVELS\ GTA5\ VEHICLES.RPF

Find and backup the 4 freight files in case you need to put them back.
You can simply drag them into a folder on your desktop.

Now click Edit mode on OpenIV

Next, delete freight+hi.ytd from the OpenIV list.

Now drage and drop the 3 freight files into the OpenIV list. 

Unclick Edit mode and you are done.


==========================OVERHAULED TRAINS================================

Rename the files to sd70ace, sd70ace_hi etc... 

Using OpenIV navigate to:

MODS\ UPDATE\ X64\ DLCPACKS\ OVERHAULEDTRAINS\ DLC.RPF\ X64\ VEHICLES.RPF

Enter EDIT mode on OpenIV and drag the 3 sd70ace files into the list to add them.

Now navigate to:

MODS\ UPDATE\ X64\ DLCPACKS\ OVERHAULEDTRAINS\ DLC.RPF\ COMMON\ DATA\ LEVELS\ GTA5

Make sure you are in EDIT mode on OpenIV.

Drag VEHICLES.META into a folder to make a backup. 

Now, right click on VEHICLES.META in the OpenIV list and select EDIT.

Add the following entry (copy/paste) just BELOW where it says <InitDatas>

<Item>
      <modelName>sd70ace</modelName>
      <txdName>sd70ace</txdName>
      <handlingId>FREIGHT</handlingId>
      <gameName>FREIGHT</gameName>
      <vehicleMakeName />
      <expressionDictName>null</expressionDictName>
      <expressionName>null</expressionName>
      <animConvRoofDictName>null</animConvRoofDictName>
      <animConvRoofName>null</animConvRoofName>
      <animConvRoofWindowsAffected />
      <ptfxAssetName>null</ptfxAssetName>
      <audioNameHash>freight</audioNameHash>
      <layout>LAYOUT_TRAIN</layout>
      <coverBoundOffsets>STANDARD_COVER_OFFSET_INFO</coverBoundOffsets>
      <explosionInfo>EXPLOSION_INFO_DEFAULT</explosionInfo>
      <scenarioLayout />
      <cameraName>DEFAULT_FOLLOW_VEHICLE_CAMERA</cameraName>
      <aimCameraName>DEFAULT_THIRD_PERSON_VEHICLE_AIM_CAMERA</aimCameraName>
      <bonnetCameraName>VEHICLE_BONNET_CAMERA_STANDARD</bonnetCameraName>
      <povCameraName>DEFAULT_POV_CAMERA</povCameraName>
      <FirstPersonDriveByIKOffset x="0.000000" y="0.000000" z="0.000000" />
      <FirstPersonDriveByUnarmedIKOffset x="0.000000" y="0.000000" z="0.000000" />
	  <FirstPersonProjectileDriveByIKOffset x="0.000000" y="0.000000" z="0.000000" />
	  <FirstPersonProjectileDriveByPassengerIKOffset x="0.000000" y="0.000000" z="0.000000" />
	  <FirstPersonDriveByLeftPassengerIKOffset x="0.000000" y="0.000000" z="0.000000" />
	  <FirstPersonDriveByRightPassengerIKOffset x="0.000000" y="0.000000" z="0.000000" />
	  <FirstPersonDriveByLeftPassengerUnarmedIKOffset x="0.000000" y="0.000000" z="0.000000" />
	  <FirstPersonDriveByRightPassengerUnarmedIKOffset x="0.000000" y="0.000000" z="0.000000" />
	  <FirstPersonMobilePhoneOffset x="0.155000" y="0.315000" z="0.520000" />
      <FirstPersonPassengerMobilePhoneOffset x="0.136000" y="0.223000" z="0.425000" />
      <PovCameraOffset x="0.000000" y="-0.100000" z="0.680000" />
      <PovCameraVerticalAdjustmentForRollCage value="0.000000" />
      <PovPassengerCameraOffset x="0.000000" y="0.000000" z="0.000000" />
      <vfxInfoName>VFXVEHICLEINFO_TRAIN_GENERIC</vfxInfoName>
      <shouldUseCinematicViewMode value="true" />
      <shouldCameraTransitionOnClimbUpDown value="false" />
      <shouldCameraIgnoreExiting value="false" />
      <AllowPretendOccupants value="true" />
      <AllowJoyriding value="true" />
      <AllowSundayDriving value="true" />
      <AllowBodyColorMapping value="true" />
      <wheelScale value="0.370000" />
      <wheelScaleRear value="0.370000" />
      <dirtLevelMin value="0.000000" />
      <dirtLevelMax value="0.900000" />
      <envEffScaleMin value="0.500000" />
      <envEffScaleMax value="0.800000" />
      <envEffScaleMin2 value="0.500000" />
      <envEffScaleMax2 value="0.800000" />
      <damageMapScale value="0.600000" />
      <damageOffsetScale value="1.000000" />
      <diffuseTint value="0x00FFFFFF" />
      <steerWheelMult value="1.000000" />
      <HDTextureDist value="5.000000" />
      <lodDistances content="float_array">
        30.000000
        55.000000
        100.000000
        200.000000
        1000.000000
        1000.000000
      </lodDistances>
      <minSeatHeight value="1.44" />
      <identicalModelSpawnDistance value="20" />
      <maxNumOfSameColor value="10" />
      <defaultBodyHealth value="1000.000000" />
      <pretendOccupantsScale value="1.000000" />
      <visibleSpawnDistScale value="1.000000" />
      <trackerPathWidth value="2.000000" />
      <weaponForceMult value="1.000000" />
      <frequency value="100" />
      <swankness>SWANKNESS_2</swankness>
      <maxNum value="999" />
      <flags>FLAG_NO_BOOT FLAG_PEDS_CAN_STAND_ON_TOP FLAG_HAS_LIVERY FLAG_GEN_NAVMESH FLAG_HEADLIGHTS_USE_ACTUAL_BONE_POS FLAG_DONT_SPAWN_AS_AMBIENT</flags>
      <type>VEHICLE_TYPE_TRAIN</type>
      <plateType>VPT_NONE</plateType>
      <vehicleClass>VC_RAIL</vehicleClass>
      <wheelType>VWT_SPORT</wheelType>
      <trailers />
      <additionalTrailers />
      <drivers>
        <Item>
          <driverName>S_M_M_Trucker_01</driverName>
          <npcName />
        </Item>
		<Item>
          <driverName>S_M_Y_Construct_01</driverName>
          <npcName />
        </Item>
		<Item>
          <driverName>S_M_Y_Construct_02</driverName>
          <npcName />
        </Item>
		<Item>
          <driverName>S_M_Y_Dockwork_01</driverName>
          <npcName />
        </Item>
      </drivers>
      <extraIncludes />
      <doorsWithCollisionWhenClosed />
      <driveableDoors />
      <bumpersNeedToCollideWithMap value="false" />
      <needsRopeTexture value="false" />
      <requiredExtras />
      <rewards />
      <cinematicPartCamera />
      <NmBraceOverrideSet />
      <buoyancySphereOffset x="0.000000" y="0.000000" z="0.000000" />
      <buoyancySphereSizeScale value="1.000000" />
      <pOverrideRagdollThreshold type="NULL" />
    </Item>


Now Click SAVE.

Now in OpenIV navigate to:

MODS\ COMMON.RPF\ DATA\ LEVELS\ GTA5

Near the bottom of the list you will find TRAINS.XML

Drag it to your folder or desktop to make a backup!

Make sure you are in edit mode on OpenIV and right click Trains.xml in the list.

Select EDIT.

You will see now the veriety of created trains in the list. 

You can add my entry into existing trains with the following:


                             <carriage
					model_name = "sd70ace"
					max_peds_per_carriage = "0"
					flip_model_dir = "false"
					do_interior_lights = "true"
					carriage_vert_offset = "1.55"
			repeat_count = "1" />

You can add this into any train config in the list. To have several spawn in a row, change the 'repeat_count' number from "1" to something else. Most I did was "4".

If you want the engine facing backwards when not leading, change flip_model_dir to TRUE. And do_interior_lights to FALSE.

After adding them to the train setups you desire, save the file. They should now appear in the mod when that particular train you added them to spawns.

Thats it, you are finished!