Cotoneaster can be worked just before bud break like most specemines. The secret is timing it and the after care available. Once worked (thawed, repotted, pruned) you can't let it refreeze without usually suffering some serious side effects. So, worked specimines need late winter protection once awoken from their winter nap. Chill die back may be planned for by prunning above the final cut line and leaving more to anticipate the die back, then another cut back in spring to your envisioned planned cut. Cotoneaster liked being cut back to fill out better with new growth during the growing season here in NJ