Cannot change Word.Application options from C# Installer Class

Question

I am developing MS-Word Add-In using Visual Studio 2019 (with C#). I am trying to make my add-in change some Word options, like this:

private void ThisAddIn_Startup(object sender, System.EventArgs e)
{
    // Set numeral to "Hindi"
    Application.Options.ArabicNumeral = WdArabicNumeral.wdNumeralHindi;
}

Although it works, it is not efficient because this code will be executed every time the Word application is opened. I need to execute it only once when my add-in is being installed , so I tried to create an Installer Class and do it like this:

public override void Install(IDictionary stateSaver)
{
    base.Install(stateSaver);

    Word.Application app_ = new Word.Application();

    // Set numeral to "Hindi"
    app_.Options.ArabicNumeral = WdArabicNumeral.wdNumeralHindi;
}

However, the second method doesn't change numeral to "Hindi".. Any help?

Note: To make sure that the Install function gets executed, I tried to divide by zero to make sure it will give runtime error.