A typical Pokémon Gen 3 save editor on Android offers a range of features, including:

Your emulator is saving in a 64KB flash format instead of 128KB, or the save sector is split incorrectly.

PKHeX is the definitive PC save editor, but it does not have a native Android app. You can use it on Android via web-based ports.

Yes, it is safe as long as you always keep a backup of your original .sav file before editing. If an edit goes wrong or you experience a bug, you can simply restore the backup.