Full repo available at https://bitbucket.org/createdbyx/codefarts.utilities-extension-methods-only

/// <summary>
/// Adds the specified source array to the end of the destination array.
/// </summary>
/// <typeparam name="T">Specifies the generic type of the array.</typeparam>
/// <param name="array">The destination array.</param>
/// <param name="sourceArray">The source array that will be added to the end of the destination array.</param>
/// <returns>Returns the resized and updated destination array.</returns>
public static T[] Add<T>(this T[] array, T[] sourceArray)
{
    if (array == null || sourceArray == null || sourceArray.Length == 0)
    {
        return array;
    }

    Array.Resize(ref array, array.Length + sourceArray.Length);
    sourceArray.CopyTo(array, array.Length - sourceArray.Length);
    return array;
}

/// <summary>
/// Adds a new extry to the end of the destination array.
/// </summary>
/// <typeparam name="T">Specifies the generic type of the array.</typeparam>
/// <param name="array">The destination array.</param>
/// <param name="value">The item that will be added to the end of the destination array.</param>
/// <returns>Returns the resized and updated destination array.</returns>
public static T[] Add<T>(this T[] array, T value)
{
    if (array == null)
    {
        return array;
    }

    Array.Resize(ref array, array.Length + 1);
    array[array.Length - 1] = value;
    return array;
}