If you sign an APK if you do a build afterwards, it stays recorded?

The option:

  

Generate Signed APK ...

is to sign the .apk using a Keystore, it is usually the key with which you would sign your applications for the Playstore.

If you wish to re-sign your .APK you must use the Generate Signed APK again option, because when you build your .APK again it is signed with a DEBUG Keystore ( the previous signature is not maintained !).

If you only use the option

  

Build APK ...

your application will only be signed with the Debug Keystore and would not be an application intended for the playstore.

The first time you create an APK you will ask for registration, but then use that same registry for the other APKs so it is not necessary to re-register another key, just give it to generate apk and you will be created in the project folder from android / app / build / outputs / apk

You must Generate the signed APK every time you are going to create a new version to publish. If you clicked Generate Signed APK and before publishing it, you realized that it was necessary to add a change, you will have to do this process again to generate the APK with those latest changes. If you already published a version of your APK in the Play Store and make changes to the code, you will have to change the versionName of this new APK in the build.gradle file (module app) that you are going to create, as well as the versionCode, since they can not match in the Play Store these values of the APK that is published and the new APK that you are going to publish.