I have a PS3 with a 500GB HDD, and a PS4 with a 1TB SSHD. The 500GB in the PS3 is from the PS4. I'd like to trade in my PS4, but want to swap the 500GB back into the PS4. To do this of course I can backup to an external USB HDD. I'd like to know if I can use the same external HDD without losing the data to the first console? For example, backup the PS3 to USB HDD, then stick the same HDD into the PS4 and back that up as well. So in the end, both the PS3 and PS4 data are on the same USB HDD, at the same time? So when I get a PS4 Pro, I can put the HDD from that into the PS3, and put the SSHD into the PS4 Pro. I hope that makes sense.