While you can use Baksmali (the disassembler) via command line to dump Smali files, edit them in Notepad++, and reassemble them, Dex Editor Plus integrates this workflow. It provides a tree view of the class hierarchy. You can navigate to com/example/MainActivity , find the onCreate method, and change a register value or a logic flag instantly.
If the app has signature verification, you may need to patch that check first. dex editor plus link
Editing Android apps can be useful in various scenarios: While you can use Baksmali (the disassembler) via