I agree with western Europe and nw Africa being useless for this mod, as it would cost lots of time and resources to properly portray them in the 'Diadochi Wars' and they would take away the focus form the main theme (imho even if those areas were entirely rebel controlled). I wasn't suggesting to make a new map, but simply to cut off most of western Europe (and possibly even the most northern and southern areas) while leaving the scale of the EBII map unchanged. I don't know anything about modding maps, but I assume choping some edges isn't a real problem. Then you would have a smaller and easier to handle map, that focuses on the regions most important for the Diadochi wars. Like in this example (map of EB1 provinces):
That would circumvent the imo quite drastic move to have Carthage, the upcoming Roman Republic and all of western Europe and it's peoples as one big rebel controlled area (if I understand you correctly), and eventual easy prey for the real factions in the Balkan/mainland Hellas.
With a map as above you would have eastern Sicily and southern Italy with it's Greek cities in the game (as strong rebel cities with garrison script?) and don't have to deal with the ancient powerhouses as Carthage, Rome, Gauls etc. being rebels. Also there's still enough room in the nw Balkan and eastern Europe for the Celtic peoples (as possible emerging faction[s]?) that will in the early 3rd century BCE invade Greece and western Anatolia.
You could even make the Romans an emerging faction with a two or three waves of spawned full stacks in nw Greece (similar the Mongols in vanilla M2TW) round about the time of the Macedonian Wars. Actually the 'emerging Rome' idea is more a joke... I just wanted to compare the aggressively expanding Romans with the dreaded Mongols.