Addendum to the NA61/SHINE Proposal: A Low-Energy Beamline at the SPS H2

This document describes our intention to build a tertiary hadron low-energy beamline at the SPS H2. The existing H2 beamline has been designed for high-energy physics, and the NA61/SHINE experiment has conducted measurements with hadron beams between 13 GeV/$c$ and 350 GeV/$c$. Recently, interest in measurements with lower energy beams down to 2 GeV/$c$ has been expressed for various physics cases. We aim to start beamline operation in 2024 and continue physics measurements with the low-energy beamline after LS3. In this document, details on this project will be presented. We want to initiate communication with the SPSC committee based on the LoI and seek an SPSC endorsement.