User\my documents\my game\ fallenenchantress\mods\

Ok, not sure, I test it and did put core improvements in user's mod, set localdateonly, use mod in game optian, odd is that I look at reseaching there is building are two time, that when I reseach those tech that had two same building, crash, I guess game don't think two file together and use one file override other core file.

Ok, Heavenfall, I did use xml file, so basic I delete whole xml file that called "CoreImprovementsTest" same as your mod. I only put in that file same command (again same as your. LOL, I find to make my mimd much understand easy that way) like this

 <ImprovementType InternalName="AdventurersGuild">
        <DisplayName>Adventurer's Guild</DisplayName>
        <Description>The Adventurer's Guild has a chance per season of giving stationed champions 1 xp.  It also reduces the cost of recruiting champions by 25%.</Description>
        <AllowedPerFaction>1</AllowedPerFaction>
        <RequiresCity>1</RequiresCity>
        <ReqCityLevel>3</ReqCityLevel>
        <BarredTerrain>River</BarredTerrain>
        <BarredTerrain>SwampTerrain</BarredTerrain>
        <PreferredTerrain>City</PreferredTerrain>
        <PreferredTerrain>Category:Land</PreferredTerrain>
        <PreferredTerrain>Forest</PreferredTerrain>
        <Prereq>
            <Type>Tech</Type>
            <Attribute>Recruiting</Attribute>
        </Prereq>
        <LaborToBuild>120</LaborToBuild>
        <GameModifier>
            <ModType>StationedUnitStatBonus</ModType>
            <StrVal>UnitStat_Experience</StrVal>
            <StrVal2>OnlyChampions</StrVal2>
            <Value>1</Value>
            <Operator>100</Operator>
            <Provides>Stationed champions have a chance of getting 1xp/season</Provides>
        </GameModifier>
        <GameModifier>
            <ModType>Player</ModType>
            <Attribute>AbilityBonus</Attribute>
            <StrVal>A_Recruiting</StrVal>
            <Value>-25</Value>
        </GameModifier>
        <GameModifier>
            <ModType>Resource</ModType>
            <Attribute>Gold</Attribute>
            <Value>-1</Value>
            <PerTurn>1</PerTurn>
        </GameModifier>
        <AIData AIPersonality="AI_General">
            <AIPriority>5</AIPriority>
            <AITag>CommandPost</AITag>
        </AIData>
        <ArtDef>Art_AdventurersGuild</ArtDef>
    </ImprovementType>

So you see, this is only simple command in that xml file in mod folder, so I test and play game reseach said two adventures guild, but no other building two on it.

so I start reseaching  those, it's seem start stop or lag, but ok once a while, no crash. once I done and I start building (I know, I set 120, it's so easy to build,I just want hurry up and see if that work) so it's was so fine, no crash, but howver, still said two time, in fact, I end up paid 2 man per turn, not 1, but it's said 1 per turn but you get two time and end up pay two time per turn. How could I solve this problem? Later many turn it's crash, I wonder if a.i build or reseaching adventures guild while this happan?

An easier solution is to replace the core file in the game directory. Make a backup copy of the original file and keep it somewhere else. Then edit the one you have in the game folder. If you are making lots of changes, this is the best way to go. 

I try that, it's didn't work and end up as duplicate building, cost that I working on.