I discovered an interesting new menu bar feature in Sierra that I hadn't even thought of looking for. The right hand menu bar elements have always been fixed in place by Apple, but in Sierra Control+Click+Drag can reorder all of the elements on the right end of the menu bar including date & time but excluding Siri and Notifications.
That's been user-adjustable for quite some time now.
As for the date thing, that only changes the output of a specific set of API calls that apps can either use or do their own thing, so only apps that
try to display the time the way the user has requested it are going to do so. Everybody else can play their own banjo.
LONG time ago I recall seeing someone post WHERE the "format string" was stored. And from there you could go in and edit it to anything you wanted. It's just using the DATE command from terminal, which is extremely robust. Sorry I don't recall where that was, and I'd wager it's moved by now.
I use this one for time stamping log entries:
command: date "+%Y/%m/%d %H:%M:%S"
outputs: 2016/10/24 12:00:03
the default format:
date (equivalent to date "+%a %b %d %T %Z %Y")
Mon Oct 24 12:00:32 CDT 2016
man date for (lots) more information, and for the geeks: date "+%s"
