You can inherit product onchange of sale order line form and and update value from product template in your new field. 

Hi,

Rather you use @api.onchange to update the sale order line field by any value you want

@api.onchange('field1', 'field2') # if these fields are changed, call method
def check_change(self):
    if self.field1 < self.field2:
        self.field3 = True # filed3 get True in the form view if field1 < field2

Or you can use related field. The field will be updated automatically by the ORM

field_x = fields.Char(related='product_id.field_x', store=True)

Best regards

Thanks for your answers.

I used a related field and it worked fine. But when I change the value of my field in order line, it also change the value in product template.