If you update the excel file a normal Load Data of the app won't work since the file is attached. You will need to go into the Load Editor and under the connections look for 'Attached Files'. Drag and drop to replace the old excel file with the newly updated one. You can then hit 'cancel' not insert script. Now hit load data and the new rows or updated data should populate.
Files are never attached in Qlik. As you know, Qlik loads the data from the file. Qlik only keeps connection data to that file. You can delete the XLS file and the app would continue working.
If the content of that XLS file changes, the only thing you need to do is run the script again.
If the name of the XLS file changes, sure, then you need to do some maintenance. But that would not be a smart way of working as that means you end up having to update your app every time you change the XLS file.
Same file, updated data? Just run the script again.