Question On Plugin System

I am using the plugin system to implement some custom business rules for some products that we sell.

I would like to add a checkbox on the product admin page to enable this new feature on the required products.

In the past I have bypassed the plugin for this and edited the core files to include the additional check box field.

I really like the plugin system and think I just must be missing something.

I would like the plugin to have all required logic implemented in its self.

Is there an example of the recommended way of implementing this using a plugin without editing the core files?

Thanks in advance for any advice that can be given!

It depends.   What is the "new feature on the required products" / what is the "required logic"?

We are using it as a reservation system.

The checkbox is similar to the isDonwloadableProduct feature.

So I want to add a isReservationProduct checkbox on the product admin page.

The required logic is already implemented in the plugin.
I am just looking for the best way to implement the update to the product object.cs and the view.cshtml.
So that I can upgrade the nopcommerce when needed and not have to patch in these additional changes.

For some simple changes like this you can change core code. And there are lots of free open source code. You can check that code.