[android-porting] Customise Pre-installed Android in personal Smartphones?

[r***@gmail.com]

How is it possible for me to look into my smartphone's Android image and
add-remove/customise the applications pre-installed with the customised
distribution in my smartphone?

I also want to copy and save some applications' saved data, like Whatsapp
chats, images and videos, in personal folders without having them backed-up
in my Google Drive.

*I don't wish to use the following:*

Creating a Google Drive backup:

Open WhatsApp.
Go to Menu Button > Settings > Chats > Chat backup.
Tap Back up to Google Drive and set up the backup frequency to your
liking.
You will be prompted to select a Google account that you will back up
your chat history to.