config: add _set_option() method to ConfigurableObject

mylib/config.py

@@ -1296,6 +1296,10 @@ class ConfigurableObject:
 
         return default if default is not None else self._defaults.get(option)
 
+    def _set_option(self, option, value):
+        """Set option value"""
+        self._kwargs[option] = value
+
     def set_default(self, option, default_value):
         """Set option default value"""
         assert option in self._defaults, f"Unkown option {option}"