Yep, you can edit the mercenaries, just look at your descr_mercenaries.txt in your campaign folder and you can find this:
pool Britain
regions Britannia_Inferior Tribus_Silurii Britannia_Superior Hibernia
unit merc barbarian infantry, exp 0 cost 800 replenish 0.06 - 0.19 max 6 initial 5
when regions are the regions in where you can find the mercenaries.
unit merc barbarian infantry is the troop
exp is the experience who they have when you hire that troop
cost is the cost
replenish 0.06 - 0.19 is the "regeneration" of troops, when this number reaches 1, a new Barbarian Mercenaries will apear in the campaign
max is the number of max troops you can hire
initial, is the number of troops you can hire at the first times.
How to add a new mercenary troop in a region:
For example we have in
pool Britain
regions Britannia_Inferior Tribus_Silurii Britannia_Superior Hibernia
unit merc barbarian infantry, exp 0 cost 800 replenish 0.06 - 0.19 max 6 initial 5
And we want to add a cretan archers here we are going to:
pool Britain
regions Britannia_Inferior Tribus_Silurii Britannia_Superior Hibernia
unit merc barbarian infantry, exp 0 cost 800 replenish 0.06 - 0.19 max 6 initial 5
we add this line (in red):
pool Britain
regions Britannia_Inferior Tribus_Silurii Britannia_Superior Hibernia unit merc cretan archers, exp 1 cost 750 replenish 0.07 - 0.15 max 12 initial 1
unit merc barbarian infantry, exp 0 cost 800 replenish 0.06 - 0.19 max 6 initial 5
And always make a backup
This maybe can be a little thing, but this can be usefull
