diff --git a/data-util.lua b/data-util.lua
index 84b7785..1dc5fef 100644
--- a/data-util.lua
+++ b/data-util.lua
@@ -54,6 +54,19 @@ function util.contains(table, sought)
   return false
 end
 
+-- Set/override a technology's prerequisites
+function util.set_prerequisite(technology_name, prerequisites)
+  local technology = data.raw.technology[technology_name]
+  if technology then
+    technology.prerequisites = {}
+    for i, prerequisite in pairs(prerequisites) do
+      if data.raw.technology[prerequisite] then
+        table.insert(technology.prerequisites, prerequisite)
+      end
+    end
+  end
+end
+
 -- Add a prerequisite to a given technology
 function util.add_prerequisite(technology_name, prerequisite)
   local technology = data.raw.technology[technology_name]
@@ -444,14 +457,19 @@ function util.replace_product(recipe_name, old, new)
 end
 
 function replace_product(recipe, old, new)
-  if recipe ~= nil and recipe.results ~= nil then
+  if recipe then
+    if recipe.main_product == old then
+      recipe.main_product = new
+    end
     if recipe.result == old then
-      recipe.results = new
+      recipe.result = new
       return
     end
-    for i, result in pairs(recipe.results) do
-			if result.name == old then result.name = new end
-			if result[1] == old then result[1] = new end
+    if recipe.results then
+      for i, result in pairs(recipe.results) do
+        if result.name == old then result.name = new end
+        if result[1] == old then result[1] = new end
+      end
     end
   end
 end
@@ -541,10 +559,10 @@ end
 
 -- Set recipe icons
 function util.set_item_icons(item_name, icons)
-  if data.raw.recipe[item_name] then
-    data.raw.recipe[item_name].icons = icons
-    data.raw.recipe[item_name].icon = nil
-    data.raw.recipe[item_name].icon_size = nil
+  if data.raw.item[item_name] then
+    data.raw.item[item_name].icons = icons
+    data.raw.item[item_name].icon = nil
+    data.raw.item[item_name].icon_size = nil
   end
 end