"How to programmatically change your Android app icon and name" for http://blog.jakelee.co.uk/programmatically-changing-app-icon

activity_main.xml

<LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        tools:context=".MainActivity">
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/red"
        android:text="Red" />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/green"
        android:text="Green" />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/blue"
        android:text="Blue" />

</LinearLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          package="uk.co.jakelee.dynamiciconchanging">

    <application
            android:label="@string/app_name"
            android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>

        <activity-alias
                android:label="Red app"
                android:icon="@mipmap/icon_red"
                android:name=".RED"
                android:enabled="true"
                android:targetActivity=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity-alias>

        <activity-alias
                android:label="Green app"
                android:icon="@mipmap/icon_green"
                android:name=".GREEN"
                android:enabled="false"
                android:targetActivity=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity-alias>

        <activity-alias
                android:label="Blue app"
                android:icon="@mipmap/icon_blue"
                android:name=".BLUE"
                android:enabled="false"
                android:targetActivity=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity-alias>
    </application>

</manifest>

MainActivity.kt

class MainActivity : AppCompatActivity() {

    enum class ICON_COLOUR { RED, GREEN, BLUE }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        red.setOnClickListener { setIcon(ICON_COLOUR.RED) }
        green.setOnClickListener { setIcon(ICON_COLOUR.GREEN) }
        blue.setOnClickListener { setIcon(ICON_COLOUR.BLUE) }
    }

    private fun setIcon(targetColour: ICON_COLOUR) {
        for (value in ICON_COLOUR.values()) {
            val action = if (value == targetColour) {
                PackageManager.COMPONENT_ENABLED_STATE_ENABLED
            } else {
                PackageManager.COMPONENT_ENABLED_STATE_DISABLED
            }
            packageManager.setComponentEnabledSetting(
                ComponentName(BuildConfig.APPLICATION_ID, "${BuildConfig.APPLICATION_ID}.${value.name}"),
                action, PackageManager.DONT_KILL_APP
            )
        }
    }
}