Sure... You can change the unit size...
- Go to your Activision/Rome - Total War/ExRM/Data folder
- Copy the export_descr_unit.txt file (in short EDU)
- Rename the Copy to something like "export_descr_unit (backup).txt". This is so you don't have to reinstal the entire game if you mess things up 
- Open the original export_descr_unit.txt file
- If you scroll down you will see:
Code:
type barb chieftain cavalry scythian
dictionary rtr_sarmatian_bodyguard_early
category cavalry
class heavy
voice_type General_1
soldier sarmatian_noble_cavalry, 8, 0, 6
mount heavy horse
mount_effect horse +1, camel -1, elephant -40
attributes sea_faring,hide_forest,general_unit,very_hardy,power_charge
formation 1.5, 4, 3, 6, 4,square
stat_health 1, 7
stat_pri 7, 26, arrow, 130, 5, missile, archery, piercing, none, 25 , 1
stat_pri_attr prec
stat_sec 10, 26, no, 0, 0, melee, blade, piercing, spear, 25 , 0.8
stat_sec_attr no
stat_pri_armour 21, 4, 0, metal
stat_sec_armour 0, 1, flesh
stat_heat 5
stat_ground -6, 0, -12, 0
stat_mental 15, low, untrained
stat_charge_dist 40
stat_fire_delay 0
stat_food 60, 300
stat_cost 2, 3000, 100, 100, 150, 600
ownership scythia
This list is different for every single unit in the game... It sais what the attack stats are, how much the unit costs, etc etc. But most importantly (for you) it tells what size the units are.
If you for example want to change the size of a unit of Hastati:
- Hit Ctrl + F
- Type hastati and hit ENTER
- You will see this list appear:
Code:
type roman hastati
dictionary rtr_roman_hastati
category infantry
class light
voice_type Light_1
soldier roman_hastati, 40, 0, 1
officer roman_early_centurion
officer roman_early_standard
mount_effect horse -2, camel -2,
attributes sea_faring,hide_forest,can_sap,very_hardy
formation 1, 2, 2, 3, 5,square,shield_wall
stat_health 1, 5
stat_pri 11, 5, pilum, 38, 2, thrown, blade, piercing, spear, 25 , 1
stat_pri_attr prec,thrown,thrown ap
stat_sec 10, 5, no, 0, 0, melee, simple, piercing, sword, 0 , 0.3
stat_sec_attr no
stat_pri_armour 4, 13, 8, metal
stat_sec_armour 0, 1, flesh
stat_heat 2
stat_ground 0, 0, 0, 0
stat_mental 18, normal, trained
stat_charge_dist 30
stat_fire_delay 0
stat_food 60, 300
stat_cost 1, 1140, 438, 104, 112, 450
ownership romans_julii
- Search for the red line.
Code:
soldier roman_hastati, 40, 0, 1
- The red number tells which size the unit is on normal unit size settings. So normally a unit of hastati has 40 men.
- If you want it to consist of for example 60 men per unit simply change the line to:
Code:
soldier roman_hastati, 60, 0, 1
- Finally save the file and test it in-game.
You can do this for all units you want to use (that's going to take some time though
). But be sure you always make back-ups!!!
And there is a max of men allowed in a unit, but I don't what what it is
Maybe someone else can tell you... I think AqD is a good one to ask for some help... He has done a lot of unit balancing for his own mini mod
For more info you can use this guide (click).
Edit:
Here is how it looks in-game after changing the unit size:
Red = original size; Blue = new size
Good luck with it 
PatricianS