"SPECIAL TRAINING"

I think the ability could work as the armours, weapons and equipments work.

They could be named as "special training" or some similar

the special training could have its cost in money, time and salary and you can give it if you want

every ability (not definitely every, but most) needs a weapon (or/and) armour (or/and) shield prerequisite on the unit

        - (for example falanx needs large shild and one handed spearlike weapon)

the unit with special training could have some ability point (like the mana), and it could use its special ability from that pool

but the prerequisite of this is the initiative check, other way it kill the balance (more)

(or don't need mana, but that case the ability must be less effective / the problem with mana using, that the AI spares its mana on easy targets and you can take an advantage on it, but its more fun and more tactical / solution can be: every unit can use its special ability once per battle)

       - so an example: you make 4 rchers, give them bow, cost (only for the exampla, not real):  160 gold, 40 materials, 12 turn, 2 gold/turn

                                 because the bow you can give them the marksmann ability (double damage): 220 golt, 40 mate, 15 turn, 3 gold/turn

so i don't want to make all the abilities, just want to show the system

i think it could work well

(and leadership could set the maximum number of units per stack, it could work like strenght, essence . . . )