To be more precise I used the following stats:

type roman triarii
dictionary roman_triarii ; Triarii
category infantry
class spearmen
voice_type Medium_1
soldier roman_triarii, 40, 0, 1
officer roman_early_centurion
officer roman_early_standard
mount_effect horse +4, chariot +4, camel +4
attributes sea_faring, hide_forest, can_sap
formation 1, 1, 2, 2, 3, square, phalanx
stat_health 1, 0
stat_pri 7, 7, no, 0, 0, melee, simple, piercing, spear, 25 ,0.73
stat_pri_attr spear
stat_sec 7, 2, no, 0, 0, melee, simple, piercing, sword, 25 ,1
stat_sec_attr no
stat_pri_armour 7, 5, 5, metal
stat_sec_armour 0, 0, flesh
stat_heat 4
stat_ground 2, 0, 0, 0
stat_mental 10, disciplined, highly_trained
stat_charge_dist 30
stat_fire_delay 0
stat_food 60, 300
stat_cost 1, 500, 210, 50, 80, 500
ownership romans julii,romans brutii,romans scipii,romans senate



type egyptian elite guards
dictionary egyptian_elite_guards ; Pharaoh's Guards
category infantry
class spearmen
voice_type Heavy_1
soldier egyptian_elite_guards_new, 40, 0, 1
officer egyptian_standard
attributes sea_faring, hide_forest, can_sap, hardy
formation 1, 1, 2, 2, 5, square
stat_health 1, 0
stat_pri 12, 8, no, 0, 0, melee, simple, piercing, spear, 25 ,1
stat_pri_attr no
stat_sec 0, 0, no, 0, 0, no, no, no, none, 25 ,1
stat_sec_attr no
stat_pri_armour 7, 7, 0, metal
stat_sec_armour 0, 0, flesh
stat_heat 1
stat_ground 2, 2, -2, -2
stat_mental 10, disciplined, highly_trained
stat_charge_dist 30
stat_fire_delay 0
stat_food 60, 300
stat_cost 2, 620, 330, 70, 100, 620
ownership egypt



And I did the following in descr_model_battle.txt:

For "soldier roman_triarii" for skeleton (which already had the value - fs_spearman) I added fs_swordsman (so it looked like fs_spearman, fs_swordsman)...

The above appears to work fine...