They aren't altering what they did because those recordings still exist and are preserved.   

They are using these recordings as a base for creating something new. It is no different from singing a song - your voice or instrument ALTERS the original folk song in the same manner that the Lomax remixes are doing. An argument could be made that Almeda Riddle ALTERED the tradition when she sang into the microphone in the first place.

Sorry to disagree, but this type of recordings is NOT a rotten shame, it is just another artist interpretation.   Folk songs are not meant to be museum pieces.