I am not entirely sure that I understand clearly what you mean by create. If you mean choose its content directly, then the present engine/scripting does not allow this.
However, the AI armies are chosen from the same army lists as the player's which are held in the ArmyList.txt file.
There is nothing to stop you making a clone of the campaign you want to play and then editing the ArmyList.txt file (in the case of ECW or IW) or adding a copy of the ArmyList.txt from PikeandShot\Core for the TYW campaign.
Your custom campaigns, once created, are found in \My Documents\My Games\PikeandShot\Campaigns.
If you make the specific army list you want add up to close to 2000 points and make the minima equal the maxima then you can effectively control the proportion of troops in that army for skirmishes exactly, as there will be no choice for the random setup to distort from your desired composition. The actual number of units of each type will be adjusted depending on the size of skirmish you choose, but the proportions will remain the same.
The engine based rules for composing army lists can be found in the BA2 documentation in
https://sites.google.com/site/battleaca ... tomization
Note that the stuff about random armies does not apply to Pike and Shot - in Pike and Shot random armies are chosen from the army lists by the AI.
In addition to the stuff discussed in the article above, there are additional items in the Pike & Shot army lists:
REGION governs which map region will be used - 0 = Germany, 1 = England, 2 = Italy.
SIDEID governs which nation the army belongs to, and hence which flag icon will be used. (You can see which is which in the Editor).
SKIN governs which unit texture folder the army's units will use.
The army name (IDS_ARMY_whatverthearmyiscalled) needs to be added to the text1.txt file in the campaign folder e.g.
IDS_ARMY_CUSTOM_ARMY, "Custom Army",
If you simply make a renamed clone of one of the existing army lists, you can alter the composition of the custom army list to your choice. Then when you select that list as the enemy army in the Skirmish selection screen, you will get to fight your custom AI army in the battle.
