Before you upload, you have the option to choose whether to keep existing merge code values or not. If you choose to keep the existing values, the Uploader will simply add the new value to the existing list, and make it the default. If you choose not to keep existing merge code values, any existing values configured for each merge code being updated will be overwritten and replaced with the latest default value. This option is always set to keep existing values unless you choose to change it.