[FIX] sale: allow adding/modifying values in sale confirmation

closes odoo/odoo#55861

Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>

addons/sale/models/sale.py

@@ -831,6 +831,12 @@ Reason(s) of this behavior could be:
 
         return True
 
+    def _prepare_confirmation_values(self):
+        return {
+            'state': 'sale',
+            'date_order': fields.Datetime.now()
+        }
+
     def action_confirm(self):
         if self._get_forbidden_state_confirm() & set(self.mapped('state')):
             raise UserError(_(
@@ -839,10 +845,7 @@ Reason(s) of this behavior could be:
 
         for order in self.filtered(lambda order: order.partner_id not in order.message_partner_ids):
             order.message_subscribe([order.partner_id.id])
-        self.write({
-            'state': 'sale',
-            'date_order': fields.Datetime.now()
-        })
+        self.write(self._prepare_confirmation_values())
         self._action_confirm()
         if self.env.user.has_group('sale.group_auto_done_setting'):
             self.action_done()