I suggest adding another field called “Line Amount”. This addition is necessary because you can’t alter the Total/Amount field easily. The Total/Amount field is connected to many calculations such as taxes and shipping costs. If you still want to make changes, you’ll have to override many methods related to “total” or “amount” in your custom app. This process requires finding and overriding those methods. However, if you just want to keep track of changes, you can use a custom field instead.