Restricting the operation of some Android buttons

I've been trying for a few days, some alternatives to locking the buttons on a tablet, and then I need them to work again. I'll show you some ways I've done and which one is working the best possible way so far.

This was the first attempt, however after a few days using it began to appear permission error to Read the file inside the system / usr folder, being that at the beginning it worked normally.

string sdCard = Android.OS.Environment.ExternalStorageDirectory.AbsolutePath;
            string path = Path.Combine(sdCard, "MyFolder/Generic.kl");

            using (StreamReader sr = new StreamReader(path))
            using (StreamReader sr = new StreamReader("/system/usr/keylayout/gpio-keys.kl"))
            {

                string line;
                //Read and display lines from the file until the end of
                //the file is reached.
            while ((line = sr.ReadLine()) != null)
                {
                    if ((line.Contains("VOLUME")) || (line.Contains("HOME")) || (line.Contains("POWER")))
                    {
                        line = $"# {line}";
                    }
                    if (line.Contains("HOME"))
                    {
                        line = $"# {line}";
                    }
                    if (line.Contains("SWITCH"))
                    {
                        line = $"# {line}";
                    }
                    if (line.Contains("VOLUME"))
                    {
                        line = $"# {line}";
                    }
                    text += line + "\n";
                }
            }
            Java.Lang.Runtime.GetRuntime().Exec("su -c rm /storage/emulated/0/MyFolder/Generic.kl");

            CreateFile();

            TransferFile();




        void CreateFile()
    {
        string sdCard = Android.OS.Environment.ExternalStorageDirectory.AbsolutePath;
        string path = Path.Combine(sdCard, "backups/gpio-keys.kll");
        // This text is added only once to the file.
        if (!System.IO.File.Exists(path))
        {
            // Create a file to write to.
            System.IO.File.WriteAllText(path, text);
        }
    }





        void TransferFile()
    {
        bool rootaccess = ExecuteAsRootBase.canRunRootCommands();
        //button.Text = rootaccess.ToString();
        if (rootaccess)
        {
            Java.Lang.Runtime.GetRuntime().Exec("su -c mount -o rw,remount,rw /system");
            Java.Lang.Runtime.GetRuntime().Exec("su -c rm system/usr/keylayout/gpio-keys.kl");
            Java.Lang.Runtime.GetRuntime().Exec("su -c mv /storage/emulated/0/backups/gpio-keys.kl system/usr/keylayout/");
            Java.Lang.Runtime.GetRuntime().Exec("su -c chmod 644 /system/usr/keylayout/gpio-keys.kl");
            Java.Lang.Runtime.GetRuntime().Exec("su -c chown system.system /system/usr/keylayout/gpio-keys.kl");
        }
    }

As I said earlier, this solution worked normally for a period of time, then denied access appeared. To leave the buttons working I used the following command, with the same logic:

if (line.Contains("HOME"))
{
    line = line.Replace("# ", "");
}

Another solution that I have adopted that is also very functional is this:

Java.Lang.Runtime.GetRuntime().Exec("su -c sed -i 's/^[^#]*VOLUME_DOWN/# &/' /system/usr/keylayout/Generic.kl");
Java.Lang.Runtime.GetRuntime().Exec("su -c sed -i 's/^[^#]*VOLUME_UP/# &/' /system/usr/keylayout/Generic.kl");

However, I could not get the "#" out of the front of the line when I put it in the same command. Does anyone understand sed command in adb shell to help me rewrite the line the way it "uncomment" this particular line?