I Decompiled and recompiled it without any edit but the app is not installed the error message :
the package appears to be corrupt,
or the package conflicts with an existing package by the same name,
Assuming the resulting apk is valid, the likely issue is that it has the same package name as one that is installed.
Android prohibits a package updating with a different signing key.
You would need either root or to be able to mount the filesystem to replace the apk in /system first.