  The shape and polarisation properties of the radio pulse profiles of
radio-loud magnetars provide a unique opportunity to investigate their
magnetospheric properties. Gaussian Process Regression analysis was used to
investigate the variation in the total intensity shape of the radio pulse
profiles of the magnetar Swift J1818.0-1607. The observed profile shape was
found to evolve through three modes between MJDs 59104 and 59365. The times at
which these transitions occurred coincided with changes in the amplitude of
modulations in the spin-down rate. The amount of linear and circular
polarisation was also found to vary significantly with time. Lomb-Scargle
periodogram analysis of the spin-down rate revealed three possibly harmonically
related frequencies. This could point to the magnetar experiencing seismic
activity. However, no profile features exhibited significant periodicity,
suggesting no simple correlations between the profile variability and
fluctuations of the spin-down on shorter timescales within the modes. Overall,
this implies the mode changes seen are a result of local magnetospheric
changes, with other theories, such as precession, less able to explain these
observations.
