You only will not be able. Сountries will refuse..\Mods\Ab_Urbe_Condita\DB\defines.txt
_COUNTRY_ALLIANCE_MAX_ = 3 #Positive; 5 (default)
So, if you get more countries at start in alliance (more than 3) there will be a crash or you only will not be able to create new alliance with more than 3 countries ?
I had made this change a long time ago, because with the default 5 in my scenarios countries went for too weird unhistorical alliances. So, it is for a kind of historisity/balance. But we can bring back the number five and try to redo the balance by working with relations.
Since I have a reason to write the post, here is the new version: https://www.mediafire.com/file/o2wl6uyvohenuf6/Ab_Urbe_Condita_next.zip/file
Sorry, but still without the new technologies. It is a difficult task, I am currently working on it, doing many tests. Here is what I did in between times:
New country — Kibyra (Cibyra Magna), great city in Asia Minor. "Cibyra alone could muster 30,000 infantry and 2000 cavalry" (no source is given in the Wikipedia on this numbers). The country can be established in any scenario in the "Prygia Pacatiana" province.
New events for Pontus (Pontic rule over Armenia Minor and Colchis; mission of Aristion), Athenae (Tyrannos Aristion), Getae (Burebista, Death of Burebista), Cyrenaica (Ophellas, Ophellas' ambitions), Aegyptus (Ptolemies and Cyrenaica), Colchis (Decentralisation in Colchis), Cibyra (Formation of the Tetrapolis). New Intelligentia Artificialis (AI) events. One Provinciae event (decline of Gerrha). One Temere (random) event (Galatian youth became mercenaries).
With every new version I improve many old events, sometimes rewrite them, fix the grammar and little by little transfer the texts of the events to the \Localisation\English\events.csv for avoiding text overflow. I noticed too late that without this, the text is cut off by the game if it exceeds a certain size.
New monarchs for Getae (Basileus Burebista), Athenae (Tyrannos Aristion), Characene, Arsacidae, Armenia Minor and Cibyra.
New leaders for Seleucidae, Athenae, Galatia, Characene, Turdetani, Getae, Atropatene, Armenia Minor, Aegyptus, Pharia, Cyrenaica, Asia, Macedonia and Rebelles.
More pictures and descriptions for countries and events. More armynames, navynames, leadernames and colonynames. No more land connestion between Euboea and Boeotia. Historical additions here and there, and balancing.
The Peloponnesian War short scenario ("431 ACN — Bellum Peloponnesiacum"):
One more country from the main scenario was included — the Ilercavones. The event for Colchis. Two events about the Malian Gulf tsunami of 426 BC. Balancing. Minor addings.
Grand scenario "89 ACN — Bella Mithridatica":
Under development. Balancing. Minor addings.
And the most important — little pine tree for Tenerife, the "Nivaria" province.