A change in DNA that is useful for one property to start with, can become useful later for a different function means a change in DNA of an organism that may have helped it to adopt to an environmental condition can also become useful for a completely different function in the future.

For example feathers in birds, a character developed and selected during natural selection because it provided insulation in cold weather have become useful in later stages for flight. Some heavy birds and reptiles also have feathers, but they do not fly. Like dinosaurs had feathers, but they could not fly