How to put a search value in Many2One filter bar

Hello, I want to add a Many2One field pointing to products to a view, and I want the field to default to only services first, but the user must be able to remove this filter and view all products by removing it from the filter bar at the top of the record searching window.

I’ve tried putting a domain on the field which works but I can’t (or don’t know how to) remove it later.

I then tried to mess with search_value since it’s used for the same purpose in other views but I didn’t succeed.

It is not supported in Tryton because we think it is not a good design because it would create confusing behavior where record can not always be selected.
Instead you can define an order so the preferred ones come first.