  Magnetar-like activity has been observed in a large variety of neutron stars.
PSR J1846-0258 is a young 327 ms radio-quiet pulsar with a large rotational
power ($\sim 8 \times 10^{36}$ erg s$^{-1}$), and resides at the center of the
supernova remnant Kes 75. It is one of the rare examples of a high magnetic
field pulsar showing characteristics both of magnetars and radio pulsars, and
can thus provide important clues on the differences in the emission mechanisms
between these two classes. In 2006, PSR J1846-0258 was detected to undergo an
outburst for the first time, accompanied by a large flux increase, millisecond
X-ray bursts, significant spectral changes and a large timing glitch. On August
1st 2020, after nineteen years of quiescent stable emission, the source
underwent a second magnetar-like outburst, which was followed up with several
observations by NICER, XMM-Newton, NuSTAR and Swift. In this work, we report on
the long-term timing and X-ray spectral properties of the source following the
2020 outburst, and place upper limits on any radio activity. We demonstrate
that the pulsed flux increased by a factor $> 6$ during the outburst, followed
by non-trivial variability in the spin-down rate. Our timing analysis shows
that the spin frequency and its derivative are clearly affected by
magnetospheric activity due to the outburst. We find hints for an oscillation
in the frequency derivative with a timescale of 50-60 days, recovering later on
to stable quiescence.
