It has been observed that after renaming CGM to GM1 and subsequently using the hero-digging tool, when you create a new save, it reverts back to the CGM format. To clarify, as my explanation might not be entirely clear: Let's say we have a save file called Save_01.CGM and we want to use the hero-digging tool: 1) Rename the save file from Save_01.CGM to Save_01.GM1; 2) Use the hero-digging tool on the Save_01.GM1 file; 3) The hero is successfully dug up, and we create a new save file, for example, Save_02. Therefore, the new save file, Save_02, will automatically be in the CGM format, so there is no need to rename anything.