Yes, the measured pH of orange juice will be different at different temperatures. In fact, the measured pH of any solution will be different at different temperatures! pH refers to the number of hydrogen ions floating around in a solution--the more hydrogen ions, the more acidic a solution is and the lower the pH. These hydrogen ions come from the breaking or disassociation of water: H₂O breaks into one hydrogen ion, H⁺, and one hydroxide ion, OH^-. The higher the temperature, the more water disassociates.

However, it's important to note that since the pH always depends on temperature, you can really only compare the pHs of different solutions if you measure them at the same temperature. For example, the pH of pure water is about 7 at room temperature, but if you heat it up to almost boiling (100 degrees C or 212 degrees F) the pH drops to 6.14. Also, the pH of pure water is always defined as the "neutral" pH at a given temperature, so a pH of 7 is only neutral at room temperature. At 100 degrees C, a pH of 6.14 is neutral! Therefore, while the pH of hot orange juice might be lower than the pH of room-temperature orange juice, if you compare the pH values relative to pure water at the same temperature the hot orange juice might not actually be more acidic.