5.1 is not the installer version, it's the cIOS version.
you found a modded version of what, the installer or the IOS ?
modded version should be released with information about what's different than the original version, or a patch, or the sources.
saying "mod" without knowing what's new or better or different is a little useless.
Maybe the "mod" is just a mod of 5.0, because 5.1 is a fix version of 5.0, so maybe hermes called it "mod" himself. almost nobody uses 5.0