No, I was suggesting using a dummy policy
. I linked that thread because Rob (R8XFT)'s post - post #4 - gives a good albeit quick run-through on how to use dummy policies to create some of the effects of the UA.
The thing you need to know is: Firaxis didn't supply us with all the built-in XML we need to create anything we want using just XML. And realistically we can't blame them, or else we're getting mad at Firaxis for not being able to predict what an enormous group of players will each individually want to tweak with their game. We have other reasons to hate on Firaxis.
That in mind, modders usually want to make a UA but its stipulations and effects can't just be coded using the XML from the <Traits> table. So modders have come up with a couple workarounds...
A QUICK INTRODUCTION TO DUMMY BUILDINGS:
The most common one is to create a "dummy" building, a building that uses XML tags not available directly to traits. The building is then, using lua or the <FreeBuilding> tag within a trait, given to the necessary cities of the player in order to create the effects of the UA not directly possible using only the Trait XML. e.g. Consider a UA where the player gets an extra 10%
from city conncections. This isn't possible just within <Traits>, but we can make a building with the TradeRouteModifier tag like Machu Picchu uses, and then plop that building in the player's capital.* Dummy buildings are usually invisible, especially in BNW mods. (There is a way to make buildings invisible, but it's restricted to BNW)
Dummy policies are a similar concept, and we use them when we need to use to use XML that is neither available from <Buildings> nor <Traits> in order to make a UA. Again, see Rob's post in the linked thread for a run-through on how the process of making a dummy policy.
So here's what I was thinking: Use Traits to make half the UA, adding +1 food to plantations and making use of the <PrereqTech> tag within <Traits>. Then use a dummy policy to do the other half of the trait, adding +1 food to plantations regardless of whether you have civil service or not. This way, you have half of the trait not constrained by <PrereqTech>. Savvy?
*In this case using Lua is actually advised, because of the way <FreeBuilding> operates. Be aware that <FreeBuilding> ignores all building requirements, such as that it must be built in a holy city or capital or what have you, unless it's a geographical constraint like needing to be built next to a river or coast, hence why Carthage doesn't get harbors in landlocked cities. Using FreeBuilding would therefore add the dummy building to every city, thereby changing the trait to "+10% gold from city connections per city", with ridiculous stacking. With lua, we can just add the building straight to and only to the capital. But that's an aside.