How to defrost effectively without unplugging?

The simplest trick is to use a bowl of hot water. You fill a bowl with very hot water (not boiling, otherwise it can shock the freezer), you put it inside and close the door. Let it work for about twenty minutes, then repeat if needed. The steam will soften the ice gradually. A hair dryer works just as well, you direct the hot air flow onto the frozen areas while keeping a good distance so you don't damage the internal walls. It takes longer but it works, you just need patience.

Another option is to place damp towels or wet newspaper against the ice and let it sit for a few hours. The moderate heat will make it melt gradually without being harsh on the appliance. Avoid aggressive metal scrapers, you risk puncturing a cooling pipe hidden behind. And honestly, the really effective defrosting is mostly about not letting the buildup get crazy - doing it once or twice a year as prevention is better than waiting till it's a solid block.