diff --git a/hermes_cli/config.py b/hermes_cli/config.py
index 03570bceba49..30a8ae4643c3 100644
--- a/hermes_cli/config.py
+++ b/hermes_cli/config.py
@@ -8097,6 +8097,20 @@ def edit_config():
     subprocess.run([editor, str(config_path)])
 
 
+def _default_value_for_key(dotted_key: str):
+    """Return the leaf value declared for *dotted_key* in ``DEFAULT_CONFIG``.
+
+    Unknown keys and non-leaf paths return ``None`` so they retain the legacy
+    best-effort coercion used by ``config set``.
+    """
+    node = DEFAULT_CONFIG
+    for part in dotted_key.split("."):
+        if not isinstance(node, dict) or part not in node:
+            return None
+        node = node[part]
+    return node if not isinstance(node, dict) else None
+
+
 def set_config_value(key: str, value: str):
     """Set a configuration value."""
     if is_managed():
@@ -8154,16 +8168,21 @@ def set_config_value(key: str, value: str):
     # _set_nested which preserves list-typed nodes; before #17876 the
     # inline navigation here silently overwrote lists with dicts.
 
-    # Convert value to appropriate type
-    if value.lower() in {'true', 'yes', 'on'}:
-        value = True
-    elif value.lower() in {'false', 'no', 'off'}:
-        value = False
-    elif value.isdigit():
-        value = int(value)
-    elif value.replace('.', '', 1).isdigit():
-        value = float(value)
+    # Preserve values for string-typed settings.  In particular, enum members
+    # such as approvals.mode="off" must not become YAML booleans.  Unknown keys
+    # retain the historical best-effort coercion behavior.
+    coerced_value: Any = value
+    if not isinstance(_default_value_for_key(key), str):
+        if value.lower() in {'true', 'yes', 'on'}:
+            coerced_value = True
+        elif value.lower() in {'false', 'no', 'off'}:
+            coerced_value = False
+        elif value.isdigit():
+            coerced_value = int(value)
+        elif value.replace('.', '', 1).isdigit():
+            coerced_value = float(value)
 
+    value = coerced_value
     _set_nested(user_config, key, value)
     # Normalize the api_base → base_url alias at set-time too (issue #8919),
     # so a fresh `hermes config set model.api_base ...` lands on the canonical
diff --git a/tests/hermes_cli/test_set_config_value.py b/tests/hermes_cli/test_set_config_value.py
index 2405b84a3814..6d31d558f157 100644
--- a/tests/hermes_cli/test_set_config_value.py
+++ b/tests/hermes_cli/test_set_config_value.py
@@ -249,6 +249,46 @@ class TestListNavigation:
         assert allowlist[1] == {"name": "bob", "role": "admin"}
 
 
+# ---------------------------------------------------------------------------
+# String-typed config values — regression tests for #47515
+# ---------------------------------------------------------------------------
+
+class TestStringTypedConfigValues:
+    @pytest.mark.parametrize("value", ["off", "on", "yes", "no", "true", "false", "01"])
+    def test_string_typed_values_are_not_coerced(self, _isolated_hermes_home, value):
+        """Values stay strings when DEFAULT_CONFIG declares the leaf as a string."""
+        set_config_value("approvals.mode", value)
+
+        import yaml
+        saved = yaml.safe_load(_read_config(_isolated_hermes_home))
+        assert saved["approvals"]["mode"] == value
+        assert isinstance(saved["approvals"]["mode"], str)
+
+    @pytest.mark.parametrize("key, value, expected", [
+        ("terminal.persistent_shell", "off", False),
+        ("approvals.timeout", "30", 30),
+    ])
+    def test_non_string_defaults_keep_existing_coercion(
+        self, _isolated_hermes_home, key, value, expected
+    ):
+        set_config_value(key, value)
+
+        import yaml
+        saved = yaml.safe_load(_read_config(_isolated_hermes_home))
+        node = saved
+        for part in key.split("."):
+            node = node[part]
+        assert node == expected
+        assert type(node) is type(expected)
+
+    def test_unknown_keys_keep_existing_coercion(self, _isolated_hermes_home):
+        set_config_value("custom.enabled", "off")
+
+        import yaml
+        saved = yaml.safe_load(_read_config(_isolated_hermes_home))
+        assert saved["custom"]["enabled"] is False
+
+
 # ---------------------------------------------------------------------------
 # Secret redaction in display output (issue #50245)
 # ---------------------------------------------------------------------------