Code:
type NE Bodyguard
dictionary NE_Bodyguard ; General's Bodyguard
category cavalry
class heavy
voice_type General
banner faction main_cavalry
banner holy crusade_cavalry
soldier NE_Bodyguard, 36, 0, 0.5
officer Feudal_Knights
mount barded horse
mount_effect elephant -4, camel -4
attributes sea_faring, hide_forest, can_withdraw, can_formed_charge, general_unit
move_speed_mod 1.5
formation 2, 4.4, 3, 6, 2, square
stat_health 1, 0
stat_pri 12, 11, no, 0, 0, melee, melee_blade, piercing, spear, 25, 1
;stat_pri_ex 0, 0, 0
stat_pri_attr no
stat_sec 9, 8, no, 0, 0, melee, melee_blade, piercing, sword, 20, 1
;stat_sec_ex 0, 0, 0
stat_sec_attr no
stat_pri_armour 10, 12, 4, metal
;stat_armour_ex 10, 12, 0, 0, 5, 6, 6, metal
stat_sec_armour 0, 0, flesh
stat_heat 7
stat_ground 0, 0, 0, 2
stat_mental 16, disciplined, highly_trained
stat_charge_dist 25
stat_fire_delay -2500
stat_food 60, 300
stat_cost 1, 4920, 3750, 95, 225, 960, 1, 280
armour_ug_levels 3, 4, 5, 6
armour_ug_models NE_Bodyguard, NE_Bodyguard_ug1, NE_Late_Bodyguard, NE_Late_Bodyguard_ug1
ownership england, scotland, france, hre, denmark, poland, hungary, normans, slave
era 0 england, scotland, france, hre, denmark, poland, hungary, normans
era 1 england, scotland, france, hre, denmark, poland, hungary, normans
;unit_info 11, 0, 32
recruit_priority_offset 20
Add in the parts in bold, and you've basically added the late upgrade as an armor upgrade.