Android has a removable app built into the data directory

First, the preparatory work:
Make_ext4fs, mkuserimg.sh, Simg2img,
Put them in the same directory as the. IMG.EXT4 (or. img) file that you want to modify

Second, the conversion source file is the IMG format (. img skipped)
Use the./simg2img src des command to convert USERDATA.IMG.EXT4 format files
Terminal input:

./simg2img USERDATA.IMG.EXT4 Userdata.img

Three, Mount image
Create a new directory to mount this IMG to use on this directory
Terminal input:

sudo mkdir usermain

Create a new directory named Usermain
Continue typing:

Mount-t Ext4-o Loop Userdata.img.ext4 usermain

After the mount is successful, you can manage the files in the IMG in the resource manager.

Iv. Modifying the contents of the image

Create an App directory in the Usermain directory and copy the built-in APK file into it.

sudo mkdir app

Five, RePack

Packaged as. img
Terminal input

777 ./make_ext4fs. /make_ext4fs-l 512m-s-a data userdata_out.img./usermain

Android has a removable app built into the data directory