This program is a graphical frontend to Modulate by Adam Clixby.
If you open a compressed .hdr, the contents will be unpacked to a temporary folder for modification, if any songs are updated you will be prompted to save when the window is closed.
If you open an unpacked .hdr, the contents will be opened and modified in-place, if any songs are updated, you will not be prompted to save when the window is closed.
To pack the loose files, you can use File > Save As.