Henry_Best, thank you for your reply and comment.
I should expand and clarify my intentions with the hacked USB cable approach, which is in fact, the way I will proceed pending no adverse concerns are voiced. To clarify, I would not be connecting to any computer with the hacked USB cables but solely use those cables to supply power from the separate regulated 5v supply which is external to my enclosure with the Arduinos. Also, these hacked cables will be short pigtails which terminate in USB female sockets. This will allow me to externally connect to unaltered USB cables which enter an enclosure and remain permanently connected to the Arduinos. When a code update is required, I can unplug the unaltered USB cable from the supply pigtail and connect to a computer long enough to do the code upload.
For operation...
Regulated supply with hacked USB cable, which terminates in a female socket... plugs into permanently mounted unaltered USB cable which plugs into the Arduino
For code updates…
The permanent mounted unaltered USB cable is unplugged from the hacked supply cable female socket and plugged into a computer. (computer… unaltered USB cable… Arduino)
More complicated than my original post but hopefully more concise.
Thanks again for your comment.