diff --git a/core/src/com/unciv/models/ModConstants.kt b/core/src/com/unciv/models/ModConstants.kt
index 3f3b97fc76..72bb9e9d25 100644
--- a/core/src/com/unciv/models/ModConstants.kt
+++ b/core/src/com/unciv/models/ModConstants.kt
@@ -2,6 +2,7 @@ package com.unciv.models
 
 class ModConstants {
     // Max amount of experience that can be gained from combat with barbarians
+    @Suppress("SpellCheckingInspection") // Pfrom is not a word ;)
     var maxXPfromBarbarians = 30
 
     // Formula for city Strength:
@@ -11,12 +12,12 @@ class ModConstants {
     //            defensiveBuildingStrength
     // where %techs is the percentage of techs in the tech tree that are complete
     // If no techs exist in this ruleset, %techs = 0.5 (=50%)
-    val cityStrengthBase = 8.0
-    val cityStrengthPerPop = 0.4
-    val cityStrengthFromTechsMultiplier = 5.5
-    val cityStrengthFromTechsExponent = 2.8
-    val cityStrengthFromTechsFullMultiplier = 1.0
-    val cityStrengthFromGarrison = 0.2
+    var cityStrengthBase = 8.0
+    var cityStrengthPerPop = 0.4
+    var cityStrengthFromTechsMultiplier = 5.5
+    var cityStrengthFromTechsExponent = 2.8
+    var cityStrengthFromTechsFullMultiplier = 1.0
+    var cityStrengthFromGarrison = 0.2
  
     // Formula for Unit Supply:
     // Supply = unitSupplyBase (difficulties.json)
@@ -24,30 +25,54 @@ class ModConstants {
     //          unitSupplyPerPopulation * amountOfPopulationInAllCities
     // unitSupplyBase and unitSupplyPerCity can be found in difficulties.json
     // unitSupplyBase, unitSupplyPerCity and unitSupplyPerPopulation can also be increased through uniques
-    val unitSupplyPerPopulation = 0.5
+    var unitSupplyPerPopulation = 0.5
 
     // The minimal distance that must be between any two cities, not counting the tiles cities are on
     // The number is the amount of tiles between two cities, not counting the tiles the cities are on.
     // e.g. "C__C", where "C" is a tile with a city and "_" is a tile without a city, has a distance of 2.
     // First constant is for cities on the same landmass, the second is for cities on different continents.
-    val minimalCityDistance = 3
-    val minimalCityDistanceOnDifferentContinents = 2
+    var minimalCityDistance = 3
+    var minimalCityDistanceOnDifferentContinents = 2
 
     // NaturalWonderGenerator uses these to determine the number of Natural Wonders to spawn for a given map size.
     // With these values, radius * mul + add gives a 1-2-3-4-5 progression for Unciv predefined map sizes and a 2-3-4-5-6-7 progression for the original Civ5 map sizes.
     // 0.124 = (Civ5.Huge.getHexagonalRadiusForArea(w*h) - Civ5.Duel.getHexagonalRadiusForArea(w*h)) / 5 (if you do not round in the radius function)
     // The other constant is empiric to avoid an ugly jump in the progression.
-    val naturalWonderCountMultiplier = 0.124f
-    val naturalWonderCountAddedConstant = 0.1f
+    var naturalWonderCountMultiplier = 0.124f
+    var naturalWonderCountAddedConstant = 0.1f
 
     // MapGenerator.spreadAncientRuins: number of ruins = suitable tile count * this
-    val ancientRuinCountMultiplier = 0.02f
+    var ancientRuinCountMultiplier = 0.02f
     // MapGenerator.spawnIce: spawn Ice where T < this, with T calculated from temperatureExtremeness, latitude and perlin noise. 
     val spawnIceBelowTemperature = -0.8f
     // MapGenerator.spawnLakesAndCoasts: Water bodies up to this tile count become Lakes
-    val maxLakeSize = 10
+    var maxLakeSize = 10
     // RiverGenerator: river frequency and length bounds
-    val riverCountMultiplier = 0.01f
-    val minRiverLength = 5
-    val maxRiverLength = 666  // Do not set < max map radius
+    var riverCountMultiplier = 0.01f
+    var minRiverLength = 5
+    var maxRiverLength = 666  // Do not set < max map radius
+
+    fun merge(other: ModConstants) {
+        if (other.maxXPfromBarbarians != defaults.maxXPfromBarbarians) maxXPfromBarbarians = other.maxXPfromBarbarians
+        if (other.cityStrengthBase != defaults.cityStrengthBase) cityStrengthBase = other.cityStrengthBase
+        if (other.cityStrengthPerPop != defaults.cityStrengthPerPop) cityStrengthPerPop = other.cityStrengthPerPop
+        if (other.cityStrengthFromTechsMultiplier != defaults.cityStrengthFromTechsMultiplier) cityStrengthFromTechsMultiplier = other.cityStrengthFromTechsMultiplier
+        if (other.cityStrengthFromTechsExponent != defaults.cityStrengthFromTechsExponent) cityStrengthFromTechsExponent = other.cityStrengthFromTechsExponent
+        if (other.cityStrengthFromTechsFullMultiplier != defaults.cityStrengthFromTechsFullMultiplier) cityStrengthFromTechsFullMultiplier = other.cityStrengthFromTechsFullMultiplier
+        if (other.cityStrengthFromGarrison != defaults.cityStrengthFromGarrison) cityStrengthFromGarrison = other.cityStrengthFromGarrison
+        if (other.unitSupplyPerPopulation != defaults.unitSupplyPerPopulation) unitSupplyPerPopulation = other.unitSupplyPerPopulation
+        if (other.minimalCityDistance != defaults.minimalCityDistance) minimalCityDistance = other.minimalCityDistance
+        if (other.minimalCityDistanceOnDifferentContinents != defaults.minimalCityDistanceOnDifferentContinents) minimalCityDistanceOnDifferentContinents = other.minimalCityDistanceOnDifferentContinents
+        if (other.naturalWonderCountMultiplier != defaults.naturalWonderCountMultiplier) naturalWonderCountMultiplier = other.naturalWonderCountMultiplier
+        if (other.naturalWonderCountAddedConstant != defaults.naturalWonderCountAddedConstant) naturalWonderCountAddedConstant = other.naturalWonderCountAddedConstant
+        if (other.ancientRuinCountMultiplier != defaults.ancientRuinCountMultiplier) ancientRuinCountMultiplier = other.ancientRuinCountMultiplier
+        if (other.maxLakeSize != defaults.maxLakeSize) maxLakeSize = other.maxLakeSize
+        if (other.riverCountMultiplier != defaults.riverCountMultiplier) riverCountMultiplier = other.riverCountMultiplier
+        if (other.minRiverLength != defaults.minRiverLength) minRiverLength = other.minRiverLength
+        if (other.maxRiverLength != defaults.maxRiverLength) maxRiverLength = other.maxRiverLength
+    }
+
+    companion object {
+        val defaults = ModConstants()
+    }
 }
diff --git a/core/src/com/unciv/models/ruleset/Ruleset.kt b/core/src/com/unciv/models/ruleset/Ruleset.kt
index b7bb762a82..7c3be3bf8f 100644
--- a/core/src/com/unciv/models/ruleset/Ruleset.kt
+++ b/core/src/com/unciv/models/ruleset/Ruleset.kt
@@ -133,6 +133,8 @@ class Ruleset {
         units.putAll(ruleset.units)
         unitTypes.putAll(ruleset.unitTypes)
         for (unitToRemove in ruleset.modOptions.unitsToRemove) units.remove(unitToRemove)
+        modOptions.uniques.addAll(ruleset.modOptions.uniques)
+        modOptions.constants.merge(ruleset.modOptions.constants)
         mods += ruleset.mods
     }
 
@@ -864,11 +866,11 @@ object RulesetCache : HashMap<String,Ruleset>() {
             baseRuleset
 
         for (mod in loadedMods.sortedByDescending { it.modOptions.isBaseRuleset }) {
-            newRuleset.add(mod)
-            newRuleset.mods += mod.name
             if (mod.modOptions.isBaseRuleset) {
                 newRuleset.modOptions = mod.modOptions
             }
+            newRuleset.add(mod)
+            newRuleset.mods += mod.name
         }
         newRuleset.updateBuildingCosts() // only after we've added all the mods can we calculate the building costs
 
diff --git a/core/src/com/unciv/ui/mapeditor/MapEditorScreen.kt b/core/src/com/unciv/ui/mapeditor/MapEditorScreen.kt
index 064781965c..c854890174 100644
--- a/core/src/com/unciv/ui/mapeditor/MapEditorScreen.kt
+++ b/core/src/com/unciv/ui/mapeditor/MapEditorScreen.kt
@@ -22,7 +22,7 @@ import com.unciv.ui.utils.*
 class MapEditorScreen(): BaseScreen() {
     var mapName = ""
     var tileMap = TileMap()
-    var ruleset = Ruleset().apply { add(RulesetCache.getVanillaRuleset()) }
+    var ruleset = RulesetCache.getVanillaRuleset()  // This will return a clone
 
     var gameSetupInfo = GameSetupInfo()
     lateinit var mapHolder: EditorMapHolder