The original question seems to imply that the user wants to open a .crd file *automatically* with some form of ChordPro software. Yes, you can set the default values for various filetypes, but you run the risk of screwing up some other application that uses the .crd file extension.

The easiest solution is to open the ChordPro app first, and then use it to open the various .crd files.

Personally, although I love Word and its editing capabilities, I would never use it to edit/print lyrics and/or chords - too many opportunities for things to go wrong with font changes, etc.