First the good news:
To get the "Scancode Map" line in the registry, paste the following into a text file with a ".reg" extension (use Notepad):
Windows Registry Editor Version 5.00
Note that no matter what version of regedit you have, the first line in the file must be as shown and a blank line must be after it. Then just double-click the file name and it will get imported into the registry automatically.
Then you can use Regedit to modify the binary data.
Now the bad news:
I have a Dell 2350 All-In-One which doesn't have a Break key and I have not been able to get this to work (with Visual Basic 6). The Dell uses keys F7-F12 as media control keys. I tried mapping to F6, which does not have any other controls mapped to it, but it still didn't work, so I am still without a Break key.
I have read posts online in which people say this method has worked for them, so I don't know if it is just a problem with Windows 8.1 or with Visual Basic 6 or with the Dell. If anyone can get it to work, I would love to hear about it.