Yes, you can use apple instead of pear for bulgogi. Apples are a great substitute for pears in this popular Korean barbecue dish due to their similar sweetness and texture. When substituting apples for pears in bulgogi, it is important that you also adjust the amount of sugar or other sweeteners that you add to the marinade. Apples are sweeter than pears, so too much sugar will make your bulgogi overly sweet. Additionally, apples have a much firmer texture than pears; therefore, if you choose to slice them into thin strips before marinating, they will require more time in the marinade to achieve the desired tenderness. But overall, apples and pears both work well as substitutes in a bulgogi marinade because they both impart sweetness and tang to the dish.