Custom Troops
There are a whole bunch of new factions to this mod and each has their own specialisation in the game. Some of the native factions, like the Rhodoks and the Swadians, seem to have been nerfed slightly to offer better gameplay with the newer ones.
When you reach Monarch status, by either capturing your first castle or building your own, you get to choose a title. This title defines the troops your kingdom will get. For example, picking the Tsar title will grant you access to the Vaegir troops and picking the King title will give you the Swadian troops.
Customisation
After you pick a title, you can train troops in your castle. The default training time is different per unit, so the Vaegir Marksmen will take a lot longer to train, about 26 days, than Vaegir Peasants.
Even though you can choose to train peasants, it's not recommended because in version 3.0 and version 4.0 of the game there is no troop progression. This means that you CAN NOT rank up your troops from peasant to Marksman or Knight.
How To Customise
Customisation can be done after you train your first troops in the castle or town. When you take them from the castle into your party, you can talk to to change their equipment.
You can't get custom troops from any villages you own.
In order to change the equipment you have to have new equipment for them. For example, if you want to give them new armour you need to have new armour with you and drag it into their inventory.
There is a cost attached to editing your troops: you pay 3x the price of the items you're giving them. There is a small bug with this function: the troops pick their own gear from the equipment you give them. For example, if you give your Marksman a bow, arrows, a sword and a shield, when you start a battle, only half your troops will have the bow and arrow equipped. The other half will start with the sword and shield and won't switch their weapons until the other archers have used up all of their arrows.
Armour is straight forward. The armor you give them is the armour they equip. However it takes a selection of the armour that is in their inventory
If, after you load a savegame, the troops equipment is reset, the author of the mod using the "Reload customisable kingdom troops manually" option in the Camp Options menu.
Important sidenote
When you give your troops more expensive armour and weapons, their recruitment price goes up as well because you'll be buying the weapons and armour ten times (once for each soldier). Think very carefully before you add expensive equipment because you might end up with troops that are too expensive to keep recruiting.