  We present three-epoch polarimetric images of the quasar 3C 454.3 obtained
with the Very Long Baseline Array at 22 and 43 GHz. 22 GHz polarized intensity
images show a sudden change in the polarization structure of a bright eastern
component (which we call the ``core,'' although it may be neither at the
upstream end of the jet nor completely stationary) over a 41-day interval,
coincident with the ejection of a new component from the core, as resolved in
the corresponding 43 GHz images. This polarization outburst is also present at
43 GHz in both the core and the new component. This may represent a rapid
change in the electric vector position angle of the ejected component from
being orthogonal to almost parallel to that of the core. About seven months
later, the new component, moving superluminally at 2.9 \pm 0.4 h^{-1} c$
(q_{\circ}=0.5) relative to the core and 3.9 \pm 0.4 h^{-1} c$ relative to a
bright stationary component about 0.6 mas west of the core --- very low
compared with previous measurements --- is found at 43 GHz to exhibit a further
rotation of 90$^{\circ}$ in the orientation of its polarization. Opacity
effects may account for the first rotation, but changes in the magnetic field
of the component and/or that of the underlying jet in the inner milliarcsecond
structure of 3C 454.3 are needed to account for the second. Polarized intensity
images of the quasar 0420 - 014, used as a calibrator, are also presented. The
polarization position angle of the core rotated between late 1994 and late
1996.
