I have seen that there are decompilers that works pretty well to show on fly code and resources of compiled APK. I'm wondering if there is a way to edit and rebuild APK classes without export all sources and resources recreating a new project manually adding all libraries resources code etc. Since the APK already contains all the needed dependencies and resources configured to work together should be possible.
Often there are apps that have small bugs that would be easy to fix if only was possible edit and rebuild APK on fly
You can use Virtuous Ten Studio that allows you to import an APK edit smali code and resources and rebuild the edited version of the APK.
(You can also configure it to show Java code but since uses a "smali to Java" approach the generated code is imperfect.)