In my experince the Carthies rarely do anything without BI.exe, (which I can't recomend strongly enough) as the AI almost never uses fleets or naval invasions.
If they had enough time (100 turns), they can became an unstoppable monster ;)

I've used the BI.exe mods for Rome Total Realism. Will this work on my saved game, or will it cause problems if I change the shortcut and resume my game in 242?
I don't know this, but look i the unofficial modding subforum, there is a thread about this issue and plenty of minimods, which inlcude BI only features like shield wall, to EB.

Diplomacy seems more sensible as well. After the fall of Taras, Epirus cheerfully took my cease fire/trade agreement offer and proceeded to conquer most of Macedonia, rather than continue to harass me, even though their foothold in Italy was gone.
This wasn't doen by EB, it's a hardcoded feature from vanilla RTW, if you cut the direct connection to your enemy (no more direct border province like in your game) they will ask for peace.