handle old config separately

ml-agents/tests/yamato/training_int_tests.py

     run_standalone_build,
     init_venv,
     override_config_file,
+    override_legacy_config_file,
     checkout_csharp_version,
     undo_git_checkout,
 )
 
     # Copy the default training config but override the max_steps parameter,
     # and reduce the batch_size and buffer_size enough to ensure an update step happens.
-    override_config_file(
-        "config/ppo/3DBall.yaml",
-        "override.yaml",
-        max_steps=100,
-        batch_size=10,
-        buffer_size=10,
-    )
+    overrides = {"max_steps": 100, "batch_size": 10, "buffer_size": 10}
+    yaml_out = "override.yaml"
+    if python_version:
+        override_legacy_config_file(
+            python_version, "config/trainer_config.yaml", yaml_out, **overrides
+        )
+    else:
+        override_config_file("config/ppo/3DBall.yaml", yaml_out, **overrides)
-        f"mlagents-learn override.yaml --force --env="
+        f"mlagents-learn {yaml_out} --force --env="
         f"{os.path.join(get_base_output_path(), standalone_player_path)} "
         f"--run-id={run_id} --no-graphics --env-args -logFile -"
     )  # noqa

ml-agents/tests/yamato/yamato_utils.py

 
     with open(dest_path, "w") as f:
         yaml.dump(configs, f)
+
+
+def override_legacy_config_file(python_version, src_path, dest_path, **kwargs):
+    """
+    Override settings in a trainer config file, using an old version of the src_path. For example,
+        override_config_file("0.16.0", src_path, dest_path, max_steps=42)
+    will sync the file at src_path from version 0.16.0, copy it to dest_path, and override the
+    max_steps field to 42 for all brains.
+    """
+    # Sync the old version of the file
+    python_tag = f"python_{python_version}"
+    subprocess.check_call(f"git checkout {python_tag} -- {src_path}", shell=True)
+
+    with open(src_path) as f:
+        configs = yaml.safe_load(f)
+
+    for config in configs.values():
+        config.update(**kwargs)
+
+    with open(dest_path, "w") as f:
+        yaml.dump(configs, f)