Re-train the decoder of an autoencoder?

Can the decoder of the pre-trained autoencoder be trained again by taking the feature vector of the Siamese Neural Network (SNN) as input?

I have trained the SNN model. Additionally, I trained autoencoder on the same dataset. The reconstruction of images is not satisfactory because of the small dataset. Now I want to take the feature vector of the SNN model(you can say the encoded part) and re-train the trained decoder of the autoencoder. My question is how can we take the feature vector from SNN and re-train the only decoder part of the autoencoder?