android - How do some apps block/replace heads-up notifications?

Question

Background

Ever since heads-up notifications appeared on Android, some people liked it for its quick handling, yet some hated it for showing on top of apps (especially games).

In order to show heads-up notifications, developers can use something like that:

    final NotificationCompat.Builder builder = new NotificationCompat.Builder(this)
            .setContentTitle("aa").setContentText("bb").setTicker("cc")
            .setColor(0xffff0000).setSmallIcon(R.mipmap.ic_launcher)
            .setLargeIcon(BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher))
            .setPriority(Notification.PRIORITY_HIGH);
    if (Build.VERSION.SDK_INT >= 21)
        builder.setVibrate(new long[0]);
    NotificationManager notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
    notificationManager.notify(1, builder.build());

Because of this, some apps came up with the idea to show ticker-text notifications that replace them somehow, just as it used to be before heads-up notifications:

https://play.google.com/store/apps/details?id=com.jamworks.noheadsup&hl=en

There are various scenarios where this could be useful. It could be, for example, useful in case of games, where full screen is used. That's because if the user is about to press the top area, and the heads-up notifications are shown, we would like to avoid accidental click on this notification.

The problem

Not only I can't find a way of how people did it, but it seems it doesn't work anymore on new versions of Android (tested on Android 7).

The only app I've found that blocks notification is this: https://play.google.com/store/apps/details?id=com.aboutmycode.NotificationsOff&hl=en

yet it doesn't convert the heads-up notifications to "normal" ones. Instead, it just blocks them all. Plus it requires root, and seems to just change the settings of the notifications to "blocked" .

The question

Is it possible to temporarily block the heads up notifications (and yet convert them to ones without heads-up notifications ) ? If so, how?

Which restrictions does it have? Can it work without root? If it's possible with root, how? How does the "NotificationsOff" work?

Maybe this ability was possible before, but now it is not?