Adding support for modcivs/extra uniques

For the first half of my food-and-drink modpack, I plan to include a few buildings (two of them will be wonders) allowed only to specific civs. Here's what I have in mind --

• The mod already includes a basic Tavern building (+1 each to Food/Happiness, plus extra Gold from alcoholic luxuries). England's version, the Pub, will also add Gold from Fish and Potato resources.
• Japan's version of the Tavern (the Izakaya) will add extra Gold from Fish and Rice.
• Japan will gain a fourth unique building as well: the Sakagura or sake brewery, replacing the Meadery that other civs can build. (Why that replacement? Because modern Japan also produces "regular" Western-style beer and should keep the basic Brewery offered in this mod...but I've never heard of the Japanese making a honey-based beverage.)
• I'm adapting the Oktoberfest wonder and restricting it to Germany only; when I add the second half of this modpack, Oktoberfest will generate extra Gold from the Baked Goods and Meat resources (to be added then) as well as Weissbier.
• Denmark will get the Feast Hall (a Happiness/Great People booster, plus some minor Defense) as a replacement for the Colosseum. It will also get Heorot (the royal hall from Beowulf) in place of Circus Maximus.

Some of these ideas are easy enough to implement based on my experience with other mods; I do have a few questions, though, before I get to this part of the code.

1. I'd like to support as many (relevant) modcivs as possible. If you'd like to see my UB's in an unofficial version of England, Japan, or Germany... please reply with the CIVILIZATION_CODENAME and the mod ID number.
2. I'd also like to support the "Third/Fourth Unique" mods; is there a way to tell my mod "If one or both of those mods are installed, give Civs A -C my uniques but let all the rest follow the rules"? Issuing a remod with a few tweaked folders seems like overkill.

As for #2: