Experiment with returning a normal value except under unusual conditions

gistfile1.cs

public static Alternate<T> Or<T>(this T normal, Func<T> provideAlternate)
{
	return new Alternate<T>(normal, provideAlternate);
}

public static Alternate<T> Or<T>(this T normal, T alternateValue)
{
	return new Alternate<T>(normal, () => alternateValue);
}

public class Alternate<T>
{
	readonly T _normal;
	readonly Func<T> _provideAlternate;

	public Alternate(T normal, Func<T> provideAlternate)
	{
		_normal = normal;
		_provideAlternate = provideAlternate;
	}

	public T When(bool alternateCondition)
	{
		if (alternateCondition)
			return _provideAlternate();

		return _normal;
	}
}

Lets me write.cs

var endDate = localTime.AddDays(7 * 4);
endDate = endDate.Or(endDate.Previous(DayOfWeek.Sunday)).When(endDate.IsNotA(DayOfWeek.Sunday));