Is it possible to run L4 Processors (CropMask/CropType) using as input L2A products downloaded from ESA Scihub ? (so no need to run sen2cor “in-house”)
Yes, you can use the L4x processors with the Sen2Cor L2A products downloaded from SciHub (or available on a local archive). Instructions are given on the SUM (p.62): http://www.esa-sen2agri.org/wp-content/uploads/resources/technical-documents/Sen2-Agri-Software-User-Manual-3.1.pdf.
Thank you Philippe!
May be you are also aware of this linked issue: Sen2Cor ProductReader ?