i do not thing so. I have successfully make available for recruit mercenary Thracians and Cretan archers for the Greeks.

The files you have to edit are

1.
export_descr_buildings.txt

adding the line below to the proper building

recruit "merc thracian" 0 requires factions { greek_cities,macedon, } and hidden_resource thrace

** this line is from RTR not from RTW (if you use RTW do not mention the hidden resource part as in RTW there isn't a hidden resource thrace.

2.

export_descr_unit.txt

type merc thracian
dictionary merc_thracian ; Thracian Mercenaries
category infantry
class light
voice_type Medium_1
soldier greek_thracoan, 40, 0, 1.2
attributes sea_faring, hide_improved_forest, mercenary_unit
formation 1.2, 1.2, 2.4, 2.4, 4, square
stat_health 1, 0
stat_pri 10, 6, no, 0, 0, melee, blade, piercing, axe, 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 2, 2, 2, flesh
stat_sec_armour 0, 0, flesh
stat_heat 1
stat_ground 2, 0, 3, 0
stat_mental 4, impetuous, untrained
stat_charge_dist 40
stat_fire_delay 0
stat_food 60, 300
stat_cost 1, 330, 130, 40, 50, 330
ownership slave, pontus

you need to find the record with the unit you and add in the ownership line the function you wont to produce the specific unit.
For example if you wont the Greek function to be able to produce Thracian Mercenaries your line must de like something that

ownership slave, pontus, greek_cities, seleucid, macedon

In this way you can recruit merc units that your function can already hire.

if you wont to change the corols of the unit then you have to wait until someone else help you on that as i can not.