I have an existing save game that I started without any expansions. Will activating expansions change anything in that game?
For changes that determine what stuff the AI gets seeded on their planets (which is a good chunk of expansion content), no.
However, once you activate the expansions, the new bonus ship types available become a possible unlock for both you and the AI. I'm not sure if any guardians are expansion specific, but if they are, activating the expansion will let the AI build those too.
A
few new building will get seeded in upon enabling expansions, but they are the exception, not the rule.
