NOTE: I made this on a game that includes the altered sprites from the Miranda Class (In the thread called 'Help with Importing ships'), I am not sure if it works without those altered sprite files.

//*********************************************************************************************************
Open 'fed_warpinA' (C:\Program Files\Activision\Star Trek Armada II Fleet Operations 3.0\Data\odf\system) and find:

replacement0class2 = "fed_ambassadorW"
replacement0class2randomweight = 4

add beneath it:

replacement0classX = "fed_nebula_sensorW"
replacement0classX = "fed_nebula_carrierW"
replacement0classX = "fed_nebula_warp1W"
replacement0classX = "fed_nebula_warp2W"

Replacing X with the number 1 higher than the ship before it.

//*********************************************************************************************************
Then find:

replacement1class1 = "fed_steamrunnerW"
replacement1class1position = 0,0,200

add beneath it

replacement1classX = "fed_nebula_warp1W"
replacement1classXposition = 0,0,200
replacement1classX = "fed_nebula_carrierW"
replacement1classXposition = 0,0,200

Replacing X with the number 1 higher than the ship before it.

//*********************************************************************************************************
Then find:

replacement2class4 = "fed_ambassadorW"
replacement2class4position = 0,0,-200

add beneath it

replacement2classX = "fed_nebula_sensorW"
replacement2classXposition = 0,0,200

Replacing X with the number 1 higher than the ship before it.