  The Milky Way stellar halo contains relics of ancient mergers that tell the
story of our Galaxy's formation. Some of them are identified due to their
similarity in energy, actions and chemistry, referred to as the "chemodynamical
space", and are often attributed to distinct merger events. It is also known
that our Galaxy went through a significant merger event that shaped the local
stellar halo during its first Gyr. Previous studies using $N$-body only and
cosmological hydrodynamical simulations have shown that such single massive
merger can produce several "signatures" in the chemodynamical space, which can
potentially be misinterpreted as distinct merger events. Motivated by these, in
this work we use a subset of the GASTRO, library which consists of several
SPH+$N$-body models of single accretion event in a Milky Way-like galaxy. Here,
we study models with orbital properties similar to the main merger event of our
Galaxy and explore the implications to known stellar halo substructures. We
find that: $i.$ supernova feedback efficiency influences the satellite's
structure and orbital evolution, resulting in distinct chemodynamical features
for models with the same initial conditions, $ii.$ very retrograde high energy
stars are the most metal-poor of the accreted dwarf galaxy and could be
misinterpreted as a distinct merger $iii.$ the most bound stars are more
metal-rich in our models, the opposite of what is observed in the Milky Way,
suggesting a secondary massive merger, and finally $iv.$ our models can
reconcile other known substructures to an unique progenitor.
