Unless your yield mapping system is really ancient and has never been updated (basically, is the old CYM system), you will be working with Flags5_0.gss.   The 3 vs. 5 is the major firmware version.   

*3_0.gss files can be edited with notepad if VERY careful, but that would likely be a waste as probably no current software would read them.

*5_0.gss files containing binary offsets and potentially checksums.    It would likely be impossible to successfully edit them with conventional tools.