These are still registry entries and are still located in the same part of the registry and still with the same way. This hasn't changed. What's changed is registering applications to show up for the new UI is a huge pain requiring multiple registry keys, however simply setting the opening application for a given filetype/protocol is quite easy: either open a .reg file with reg.exe (pops up a code window) or regedit,exe (pops up a prompt), or add the entry programmatically (silent).

Personally, I'm still annoyed that removed the File Types settings in Windows 7(?), though some of them have made their way back with the new settings.