Have an application with an Arduino Due, available power in the project is +24VDC and +5VDC, do not have 9V for the 2.1mm power connector. Can not really use either of the USB ports as they are needed for data connections (not all the time). Can +5VDC be applied to the 5V pins of the board as the always connected power source? Basically need to push power in the back door as power is not always on the front door connections (2.1mm or USB).
Yes. Connect diode (1N4001) from 5V (anode) to Vin (cathode) to prevent reverse driving the regulator.