How to customize lock-screen date format?

I want my lock screen's date format to be abbreviated day, day number, then year. Can this be done? I know about the Registry LocaleInfo's TimeFormat key that controls the time format, but it doesn't seem to affect my Lock screen at all. I'd also like to see AM | PM in the time. It never shows, even though my key has h:mm:ss tt, with neither seconds nor AM | PM appearing.

What about the date? I'd like the date to show as, for example, "Sat. 16 May, 2015," and a long-name month as, e.g., "Fri., 25 Sep., 2015."

Swipe down on the right side of your screen, or go to "Search" from the Start Menu. Search for "PC Settings" and choose the purple and white gear icon. On the left side look for "Time and Language." Click that and then make sure from there "Date and Time" is selected on the left. On the right side, at the bottom, select "Change date and time formats"
The lockscreen is not very customizable, but you should be able to get the date changed from there.