  The stability (or instability) of finite sized magnetic island could play a
significant role in disruption avoidance or disruption mitigation dynamics.
Especially, various current and pressure profile modifications, such as the
current drive and heating caused by electron cyclotron wave, or the radiative
cooling and current expulsion caused by the Shattered Pellet Injection could be
applied within the island to modify its stability, thus change the ensuing
dynamics. In this study, we calculate the mode structure modification caused by
such profile changes within the island using the perturbed equilibrium
approach, thus obtain the change of stability criterion $\gD'$ and assess the
corresponding quasi-linear island stability. The positive helical current
perturbation is found to always stabilize the island, while the negative one is
found to do the opposite, in agreement with previous results. The pressure bump
or hole within the island has a more complicated stability impact. In the small
island regime, its contribution is monotonic, with pressure bump tends to
stabilize the island while pressure hole destabilizes it. This effect is
relatively weak, though, due to the cancellation of the pressure term's odd
parity contribution in the second derivatives of the mode structure. In the
large island regime, such cancellation is broken due to the island asymmetry,
and the pressure contribution to stability is manifested, which is
non-monotonic. The stability analysis in this paper helps to more accurately
clarify the expected island response in the presence of profile modifications
caused by disruption avoidance or mitigation systems.
