изменить формат даты на экране блокировки Win 8.1

Yes, it is possible to change the lock screen date format.

You will need Microsoft Locale Builder.

Resources

Read about locales here:

• Custom Locales (Windows) - MSDN:
  https://msdn.microsoft.com/en-us/library/windows/desktop/dd317785(v=vs.85).aspx

Download Microsoft Locale Builder here:

• Download Locale Builder 2.0 from Official Microsoft Download Center:
  http://go.microsoft.com/fwlink/p/?linkid=96654

Instructions

1. Locale Builder > Next > Dates > Long Date Patterns > Lock screen date pattern: dddd, d MMMM
2. Then, go to Build > Build Zip Batch File > Save.
3. Extract the ZIP file.
   • You can see that the generated LDML file contains the element msLocale:lockScreenFormat.
4. Run the CMD file within an administrator command prompt.

Apply locale

If you do not see any changes after installing the custom locale, you may need to apply the custom locale or reset your region settings.

Windows 10 and newer:

• Settings > Time and language > Date & time > Additional date, time, & regional settings > Under "Region", click "Change date, time, or number formats" > Additional settings... > Reset > Yes > OK > OK.

Windows 8 and earlier:

• Control Panel > Under "Clock, Language, and Region", click "Change date, time, or number formats" > Additional settings... > Reset > Yes > OK > OK.

Windows:

• Start > Run > intl.cpl > Additional settings... > Reset > Yes > OK > OK.

Notes and limitations

• If you are missing the day of the week, month, or day notation, the lock screen will discard the custom date format pattern, and the lock screen will format manually with the full month name, comma, space, and the partial month day (element msLocale:monthDay; Dates > Partial Date Patterns > Month day pattern) pattern.

  The following symbols work:

  | Symbol | Meaning | Presentation | Example | |--------|-----------------|--------------|----------| | M | Month in year | Text, number | July, 07 | | d | Day in month | Number | 10 | | t | AM/PM marker | Text | PM | | G | Era designator | Text | AD | | ' | Escape for text | Delimiter | | 

  The following symbols do not work:

  | Symbol | Meaning | Presentation | Example | |--------|----------------------|--------------|---------| | y | Year | Number | 2009 | | h | Hour in AM/PM (1-12) | Number | 12 | | H | Hour in day (0-23) | Number | 0 | | m | Minute in hour | Number | 30 | | s | Second in minute | Number | 55 | 

• Microsoft Locale Builder only supports pattern values less than or equal to 79 characters:

  The property 'LockScreenDatePattern' must be less than or equal to 79 characters in length.

• You can have multiple repeating patterns.

• Long patterns will be wrapped onto the next line on the lock screen.

Yes you can. Thanks to the link cybermonkey provided, you can change the format in the registry:

1. Press WIN+R keys to launch RUN dialog box. Type regedit and press Enter. It'll open Registry Editor.

2. Now go to following key:

   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\SystemProtectedUserData 

3. Under SystemProtectedUserData key, you'll see a key with the name similar to S-1-5-21-x-x-x-x. Under this key, navigate to:

   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\SystemProtectedUserData\S-1-5-21-x-x-x-x\AnyoneRead\LocaleInfo 

4. The LocaleInfo key is the one which we require to change the lock screen date and time format. This key contains all the required information which was stored in INI file in Windows 8 testing builds.

5. Click on LocaleInfo key

...

7. If your Windows 8 lock screen shows time in 24-hour format, then the "TimeFormat" String in your Windows 8 Registry would be set to HH:mm tt. Change it to hh:mm tt and it'll start showing the time in 12-hour format.