Deleting user or product from a pretrained model

How can this be done with LightFM? Imagine you have a very good model already trained, and you discontinue a large group of products, and also some of your users deleted their accounts. How can this user and items representations be deleted from the model in order to avoid having to train a new model without them?

The issue names no files, tests, or entry points. Start by tracing how LightFM stores pretrained user and item representations, then determine whether removing users and products can be supported without retraining; done would be a documented, tested approach or a clear statement that retraining is required.

Written by the indexing model from the issue text.