For a beef stock, why should I roast bones at 450?
This idea is to use the Maillard reaction (the reaction between amino acids and sugars as meats are heated and browned) to enhance and concentrate flavors. The reaction begins at about 280 degrees Fahrenheit, and tops out at 330 degrees Fahrenheit, so, you could use a lower oven. It would take longer. Caramelization flavors are more pronounced at higher temperatures.   As long as your bones are well-browned, you will be in good shape. A lower temperature doesn't necessarily prevent burning, keeping any eye on your product is a better strategy.