Keras Model question for Pre trained model extension

Question

I want to add a few more layers to a Resnet50 model and my question is - do I need to compile it and train it on new data or can I just use it as it is? Will it just give me the Resnet50 results?

Here is what I am trying:

def base_model():
resnet = resnet50.ResNet50(weights="imagenet", include_top=False)
x = resnet.output
x = Conv2D(128, (3, 3), activation='relu',padding='same')(x)
x = Conv2D(128, (3, 3), activation='relu',padding='same')(x)
x = MaxPooling2D((2, 2), strides=(2, 2))(x)
x = Conv2D(256, (3, 3), activation='relu',padding='same')(x)
x = Conv2D(256, (3, 3), activation='relu',padding='same')(x)
x = MaxPooling2D((2, 2), strides=(2, 2))(x)
x = Conv2D(512, (3, 3), activation='relu',padding='same')(x)
x = Conv2D(512, (3, 3), activation='relu',padding='same')(x)
x = MaxPooling2D((2, 2), strides=(2, 2))(x)
x = GlobalAveragePooling2D()(x)
x = Dense(4096, activation='relu')(x)
x = Dropout(0.6)(x)
x = Dense(4096, activation='relu')(x)
x = Dropout(0.6)(x)
x = Lambda(lambda  x_: K.l2_normalize(x,axis=1))(x)
return Model(inputs=resnet.input, outputs=x)

And then use it like this :

enhanced_resnet = base_model()
img = image.load_img(file, target_size=(224, 224))
img = image.img_to_array(img)
x = resnet50.preprocess_input(img)
x = np.array([x])
feature = enhanced_resnet.predict(x)

What I want as return value is the features from the image and not a prediction, as I am using a distance equation to tell the similarity between images.