Small improvements,

docs/topics/spiders.rst

@@ -142,7 +142,8 @@ scrapy.Spider
            method, which is handy if you want to modify them based on
            arguments. As a consequence, these settings aren't the final values
            as they can be modified later by e.g. :ref:`add-ons
-           <topics-addons>`. The settings become final when the spider starts.
+           <topics-addons>`. The final settings are available in the
+           :meth:`start_requests` method and later.
 
        :param crawler: crawler to which the spider will be bound
        :type crawler: :class:`~scrapy.crawler.Crawler` instance

scrapy/addons.py

@@ -19,7 +19,7 @@ class AddonManager:
         self.crawler: "Crawler" = crawler
         self.addons: List[Any] = []
 
-    def apply_settings(self, settings: Settings) -> None:
+    def load_settings(self, settings: Settings) -> None:
         """Load add-ons and configurations from a settings object and apply them.
 
         This will load the add-on for every add-on path in the

scrapy/crawler.py

@@ -79,7 +79,6 @@ class Crawler:
 
         self._init_reactor: bool = init_reactor
         self.crawling: bool = False
-        self._settings_loaded: bool = False
         self._started: bool = False
 
         self.extensions: Optional[ExtensionManager] = None
@@ -95,11 +94,10 @@ class Crawler:
             install_scrapy_root_handler(self.settings)
 
     def _apply_settings(self) -> None:
-        if self._settings_loaded:
+        if self.settings.frozen:
             return
-        self._settings_loaded = True
 
-        self.addons.apply_settings(self.settings)
+        self.addons.load_settings(self.settings)
         self.stats = load_object(self.settings["STATS_CLASS"])(self)
 
         handler = LogCounterHandler(self, level=self.settings.get("LOG_LEVEL"))