If you'd like to increase the size of any particular unit in the game, scroll to the /AOW/DataLight/TypeWarriorLazy/Unites directory and choose the file corresponding to the unit whose size you would like to increase.
Inside the file, navigate to the unit's main TypeWarrior export function (in the case of the US Abrams tank, it's export TypeWarrior_AoW_US_Abrams is TypeWarrior_AOW_VehiculeTireur_NiveauBlessure, but it will be different for each unit and it may not necessarily be at the top of the file). Once located, place the following code at the beginning of the routine:
[ TGraphicCarac_LauncherEffet ( Effet = TScaleModificator ( ScaleX = 1.5 ScaleY = 1.5 ScaleZ = 1.5 ) ) ]
To increase or decrease the unit's scale relative to the original, simply modify those numbers (1.5 actually makes the Abrams really rather big, so I could try 1.2 next time). Theoretically this should work on buildings too; infact, anything in the game that has a model. It should also be possible to make units smaller by giving the scale numbers values less than 1.0.
Many thanks to Stof for the code.