When you need to temporarily replace someone or something, you can use different synonyms for the phrase "stand in for." You can "substitute," "take over," or "act as a replacement" for someone or something else. You can also "fill in," "cover," or "hold the fort" for a particular task or responsibility. Moreover, you can use "represent," "stand for," or "personate" when referring to a person, idea, or concept. In summary, when you need to describe someone or something that is taking the place of another, you can use an array of synonyms that fit your writing style and context.