I have 2 models

model_A and model_B

There's a One2many relationship among them, meaning one record in model_A can have several related records in model_B

I have a form view on model_A showing, among other things, a list of related records in model_B, like this

In the grid showing the list of related records, there' a "Add line" link

I'd like to customize the action called by clicking that link

Because I'd like to populate some fields in the new model_B record (depending on values in some fields in model_A)

I'm not sure how to do that