Good news you won't have to replay your campaign! If need to tweak battles because they take too long go into mods/EBII/data/battle_config.xml, search this line: combat-balancing. Tweak 0.22 valor to whatever you like. I made a test dacian falxman vs camilian hastati with EB2 settings it takes around 8:30 min for the romans to flee, with 1.0 battle is 6 minutes shorter.
Code:
<combat-balancing>
<missile-target-accuracy>
<infantry>1.0</infantry>
<cavalry>1.0</cavalry>
<elephants>1.0</elephants>
</missile-target-accuracy>
<melee-hit-rate>1.0</melee-hit-rate>
</combat-balancing>