Thanks for the reply, so am I right in saying that it would be safe to use these 3 pins to fire external relays etc and not have any issues? thanks again
Nope.1) You would need to recompile a unique Arduino core to remove the references to all three of those pins. It would be painful and break future compatibility, not worth the hassle IMO.2) You need to be careful with your I/O pin selection on the sam3x8. This is not a typical AVR device that can sink/source 20+ ma out of any pin, you've got both high and low current pins where high is source 15ma (Max), sink 9 and low current pins that can only source 3 and sink 6. That is detailed on the pinout diagram in your other post.3) All three pins you reference are low current pins and D72/D73 have led's hanging on the pins and are not broken out to headers. You'd have solder wires to led pads for access to those pins.