Your Alpha can be seen in Mass Storage Mode can't it? If so, just change the basemap by replacing the current gmapbmap.img [keep a backup]. The RGN method described in that thread is only for units which use only flashable regions and don't have a file system visible by PC in MSM.

You can get the Atlantic V2 image file here: [Only registered and activated users can see links. ] [6,762,496 bytes extracted]. Or the much larger Atlantic V3 here: [Only registered and activated users can see links. ] [13,123,584 bytes extracted].