The ISO8601 Standard YYYY-MM-DD format is already available in most common PC software but the option to use it must be enabled. Do this.
So far I have solved all the problems on my own system by adding COUNTRY=002 in config.sys and modifying the International section of Windows setup to use YMD, Century date on, leading zero day, leading zero month, separator minus (-). 24 hour mode Time. And I have a plan for my BIOS tickover.
Configure and use full 4 digit years in applications and observe the results of their interactions. Old form date inputs and displays are OK (cosmetic) if internal binary dates are used and operate correctly. (See the Cinderella Accceptability Index).