I run this to unify the Factoriopedia entries into a single entry.
The point is to make a recipe with the same name as the item, and then point the other recipes to it.
And then finally update the technology effects.

if mods["carbon-steel"] then
    local recipe = nil
    local technology = nil

    recipe = table.deepcopy(data.raw["recipe"]["steel-mixture-carbon"])
    recipe.name = "steel-mixture"
    data.extend({ recipe })

    recipe = data.raw["recipe"]["steel-mixture-carbon"]
    recipe.hidden = true

    recipe = data.raw["recipe"]["steel-mixture-coal"]
    recipe.factoriopedia_alternative = "steel-mixture"

    recipe = data.raw["recipe"]["steel-mixture-iron-plate"]
    recipe.factoriopedia_alternative = "steel-mixture"

    technology = data.raw["technology"]["steel-processing"]
    table.insert(technology.effects, { type = "unlock-recipe", recipe = "steel-mixture" })
end

To address the casting recipe, this is run inside the above if-then:

    if mods["space-age"] then
        recipe = data.raw["recipe"]["casting-steel"]
        recipe.ingredients = {
            {
                amount = 25, -- vanilla is 30
                fluidbox_multiplier = 10,
                name = "molten-iron",
                type = "fluid"
            },
            {
                amount = 1,
                name = "carbon",
                type = "item"
            }
        }
    end