I use Keyboard layout manager, which is free for the simpler versions. Other programs include the Microsoft Keyboard Layout Creator, which is free but not as good in my opinion.

Virtual key code editing (or resolving in the free version) - although you can get by if you are happy to hand edit the generated file. Also, I feel the interface is a lot nicer, especially if you tinker a bit. For instance, there is no export step, just save and reboot.

The non-free version has many other advantages. Caps lock special settings, special key editing (space, tab, return). Ligatures and dead keys. There's more stuff, but to be honest I can't remember exactly what features the Microsoft tool has so I don't want to risk spreading misinformation.