it is changed in compile time

we can't change module attributes and endpoint settings in runtime

lib/mix/tasks/pleroma/config.ex

@@ -0,0 +1,68 @@
+defmodule Mix.Tasks.Pleroma.Config do
+  use Mix.Task
+  alias Mix.Tasks.Pleroma.Common
+  alias Pleroma.Repo
+  alias Pleroma.Web.AdminAPI.Config
+  @shortdoc "Manages the location of the config"
+  @moduledoc """
+  Manages the location of the config.
+
+  ## Transfers config from file to DB.
+
+      mix pleroma.config migrate_to_db
+
+  ## Transfers config from DB to file.
+
+      mix pleroma.config migrate_from_db ENV
+  """
+
+  def run(["migrate_to_db"]) do
+    Common.start_pleroma()
+
+    if Pleroma.Config.get([:instance, :dynamic_configuration]) do
+      Application.get_all_env(:pleroma)
+      |> Enum.reject(fn {k, _v} -> k in [Pleroma.Repo, :env] end)
+      |> Enum.each(fn {k, v} ->
+        key = to_string(k) |> String.replace("Elixir.", "")
+        {:ok, _} = Config.update_or_create(%{key: key, value: v})
+        Mix.shell().info("#{key} is migrated.")
+      end)
+
+      Mix.shell().info("Settings migrated.")
+    else
+      Mix.shell().info(
+        "Migration is not allowed by config. You can change this behavior in instance settings."
+      )
+    end
+  end
+
+  def run(["migrate_from_db", env]) do
+    Common.start_pleroma()
+
+    if Pleroma.Config.get([:instance, :dynamic_configuration]) do
+      config_path = "config/#{env}.migrated.secret.exs"
+
+      {:ok, file} = File.open(config_path, [:write])
+
+      Repo.all(Config)
+      |> Enum.each(fn config ->
+        mark = if String.starts_with?(config.key, "Pleroma."), do: ",", else: ":"
+
+        IO.write(
+          file,
+          "config :pleroma, #{config.key}#{mark} #{inspect(Config.from_binary(config.value))}\r\n"
+        )
+
+        {:ok, _} = Repo.delete(config)
+        Mix.shell().info("#{config.key} deleted from DB.")
+      end)
+
+      File.close(file)
+      System.cmd("mix", ["format", config_path])
+    else
+      Mix.shell().info(
+        "Migration is not allowed by config. You can change this behavior in instance settings."
+      )
+    end
+  end
+end

lib/mix/tasks/pleroma/emoji.ex

@@ -55,15 +55,13 @@ defmodule Mix.Tasks.Pleroma.Emoji do
   are extracted).
   """
 
-  @default_manifest Pleroma.Config.get!([:emoji, :default_manifest])
-
   def run(["ls-packs" | args]) do
     Application.ensure_all_started(:hackney)
 
     {options, [], []} = parse_global_opts(args)
 
     manifest =
-      fetch_manifest(if options[:manifest], do: options[:manifest], else: @default_manifest)
+      fetch_manifest(if options[:manifest], do: options[:manifest], else: default_manifest())
 
     Enum.each(manifest, fn {name, info} ->
       to_print = [
@@ -88,7 +86,7 @@ defmodule Mix.Tasks.Pleroma.Emoji do
 
     {options, pack_names, []} = parse_global_opts(args)
 
-    manifest_url = if options[:manifest], do: options[:manifest], else: @default_manifest
+    manifest_url = if options[:manifest], do: options[:manifest], else: default_manifest()
 
     manifest = fetch_manifest(manifest_url)
 
@@ -298,4 +296,6 @@ defmodule Mix.Tasks.Pleroma.Emoji do
 
     Tesla.client(middleware)
   end
+
+  defp default_manifest, do: Pleroma.Config.get!([:emoji, :default_manifest])
 end

lib/mix/tasks/pleroma/instance.ex

@@ -30,6 +30,7 @@ defmodule Mix.Tasks.Pleroma.Instance do
   - `--dbuser DBUSER` - the user (aka role) to use for the database connection
   - `--dbpass DBPASS` - the password to use for the database connection
   - `--indexable Y/N` - Allow/disallow indexing site by search engines
+  - `--db-configurable Y/N` - Allow/disallow configuring instance from admin part
   """
 
   def run(["gen" | rest]) do
@@ -48,7 +49,8 @@ defmodule Mix.Tasks.Pleroma.Instance do
           dbname: :string,
           dbuser: :string,
           dbpass: :string,
-          indexable: :string
+          indexable: :string,
+          db_configurable: :string
         ],
         aliases: [
           o: :output,
@@ -101,6 +103,14 @@ defmodule Mix.Tasks.Pleroma.Instance do
           "y"
         ) === "y"
 
+      db_configurable? =
+        Common.get_option(
+          options,
+          :db_configurable,
+          "Do you want to be able to configure instance from admin part? (y/n)",
+          "y"
+        ) === "y"
+
       dbhost =
         Common.get_option(options, :dbhost, "What is the hostname of your database?", "localhost")
 
@@ -144,7 +154,8 @@ defmodule Mix.Tasks.Pleroma.Instance do
           secret: secret,
           signing_salt: signing_salt,
           web_push_public_key: Base.url_encode64(web_push_public_key, padding: false),
-          web_push_private_key: Base.url_encode64(web_push_private_key, padding: false)
+          web_push_private_key: Base.url_encode64(web_push_private_key, padding: false),
+          db_configurable?: db_configurable?
         )
 
       result_psql =

lib/mix/tasks/pleroma/sample_config.eex

@@ -16,7 +16,8 @@ config :pleroma, :instance,
   notify_email: "<%= notify_email %>",
   limit: 5000,
   registrations_open: true,
-  dedupe_media: false
+  dedupe_media: false,
+  dynamic_configuration: <%= db_configurable? %>
 
 config :pleroma, :media_proxy,
   enabled: false,