Using a transformer (estimator) to transform the target labels in sklearn.pipeline

Question

I understand that one can chain several estimators that implement the transform method to transform X (the feature set) in sklearn.pipeline. However I have a use case where

Answer 1

No, pipelines will always pass y through unchanged. Do the transformation outside the pipeline.

(This is a known design flaw in scikit-learn, but it's never been pressing enough to change or extend the API.)