Enable root modifications

Though I can not see why you would want to.....
But there's no reason you would not be able to

processor/json.go

@@ -147,6 +147,52 @@ func (p *JSONProcessor) ProcessContent(content string, pattern string, luaExpr s
 
 // updateJSONValue updates a value in the JSON structure based on its JSONPath
 func (p *JSONProcessor) updateJSONValue(jsonData interface{}, path string, newValue interface{}) error {
+	// Special handling for root node
+	if path == "$" {
+		// For the root node, we'll copy the value to the jsonData reference
+		// This is a special case since we can't directly replace the interface{} variable
+
+		// We need to handle different types of root elements
+		switch rootValue := newValue.(type) {
+		case map[string]interface{}:
+			// For objects, we need to copy over all keys
+			rootMap, ok := jsonData.(map[string]interface{})
+			if !ok {
+				// If the original wasn't a map, completely replace it with the new map
+				// This is handled by the jsonpath.Set function
+				return jsonpath.Set(jsonData, path, newValue)
+			}
+
+			// Clear the original map
+			for k := range rootMap {
+				delete(rootMap, k)
+			}
+
+			// Copy all keys from the new map
+			for k, v := range rootValue {
+				rootMap[k] = v
+			}
+			return nil
+
+		case []interface{}:
+			// For arrays, we need to handle similarly
+			rootArray, ok := jsonData.([]interface{})
+			if !ok {
+				// If the original wasn't an array, use jsonpath.Set
+				return jsonpath.Set(jsonData, path, newValue)
+			}
+
+			// Clear and recreate the array
+			*&rootArray = rootValue
+			return nil
+
+		default:
+			// For other types, use jsonpath.Set
+			return jsonpath.Set(jsonData, path, newValue)
+		}
+	}
+
+	// For non-root paths, use the regular Set method
 	err := jsonpath.Set(jsonData, path, newValue)
 	if err != nil {
 		return fmt.Errorf("failed to update JSON value at path '%s': %w", path, err)