@Override
    public void preprocess(ServiceModel serviceModel) {

        if (renameShapes == null || renameShapes.isEmpty()) return;
        // sanity check
        for (Entry<String, String> entry : renameShapes.entrySet()) {

            String originalName = entry.getKey();
            String newName = entry.getValue();
            Shape originalShape = serviceModel.getShapes().get(originalName);

            if (originalShape == null) {
                throw new IllegalStateException(
                        String.format("Cannot find shape [%s] in the model when processing "
                                + "customization config renameShapes.%s", originalName, originalName));
            }
            if (serviceModel.getShapes().containsKey(newName)) {
                throw new IllegalStateException(
                        String.format("The shape [%s] for the new name is already in the model when processing "
                                + "customization config renameShapes.%s", newName, originalName));
            }
        }

        for (Entry<String, Shape> entry : serviceModel.getShapes().entrySet()) {
            String shapeName = entry.getKey();
            Shape shape = entry.getValue();

            preprocess_RenameMemberShapes(shapeName, shape);
        }
        for (Operation operation : serviceModel.getOperations().values()) {

            if (operation.getInput() != null) {
                preprocess_RenameInputShape(operation.getInput());
            }
            if (operation.getOutput() != null) {
                preprocess_RenameOutputShape(operation.getOutput());
            }
            if (operation.getErrors() != null) {
                for (ErrorMap error : operation.getErrors()) {
                    preprocess_RenameErrorShape(error);
                }
            }
        }
        for (Entry<String, String> entry : renameShapes.entrySet()) {
            String originalName = entry.getKey();
            String newName = entry.getValue();

            Shape shape = serviceModel.getShapes().remove(originalName);
            serviceModel.getShapes().put(newName, shape);
        }
    }
Rename shapes for Member, Input, Output, ErrorMap, as well as the key for two maps:
serviceModel.shape() and shapeModifiers
aws-java-sdk-code-generator/src/main/java/com/amazonaws/codegen/customization/processors/RenameShapesProcessor.java