  Using the ARTEMIS set of 45 high-resolution cosmological simulations, we
investigate a range of merger-induced dynamical transformations of Milky
Way-like galaxies. We first identify populations of accreted stars on highly
radial orbits, similar to the 'Gaia Sausage' in the Milky Way. We show that
$\approx1/3$ of the ARTEMIS galaxies contain a similar feature, and confirm
that they usually comprise stellar debris from the most massive accreted
satellite. Selecting 15 galaxies with discs at the present-day, we study their
changes around the times of the GS-like mergers. Dark matter haloes of many of
these exhibit global changes in shape and orientation, with almost half
becoming significantly more spherical when the mergers occur. Focusing on the
galaxies themselves, we find that 4/15 have stellar discs which experience
large changes in the orientation of their angular momentum (AM) axes, at rates
of up to $\sim60$ degrees Gyr$^{-1}$. By calculating the orbital angular
momentum axes of the satellites before they are accreted, we show that there is
a tendency for the disc's AM to become more aligned with this axis after the
merger. We also investigate the origin of in situ retrograde stars, analogous
to the 'Splash' in the Milky Way. Tracing them back to earlier snapshots, we
demonstrate that they were often disrupted onto their extreme orbits by
multiple early mergers. We also find that the total mass of these stars outside
the central regions positively correlates with the total accreted stellar mass.
