How to override OrderService by plugin:
1. Create your custom new class derived from OrderService
If we prepare new class in this way:
public class MyOrderService : IOrderService
We need to implement all methods from interface IOrderService
If we prepare our new class based on OrderService, we can override only required public methods.
public class MyOrderService : OrderService, IOrderService
2. Override the DeleteOrder method
3. Create a new class, which will implement from IDependencyRegistrar. Set its "Order" property to higher value so it's run after the default one
public class DependencyRegistrar : IDependencyRegistrar
4. Register your new custom class as IOrderService.