I have a seployed web app which uses, internally, a number of Excel files, from where it reads some data. During runtime, I would like the user to be able to download one of those files, modify some data at wish and upload the modified file. The app should then be using that modified file instead of the initial one. Additionally, I want the modified file to persist across different runs of the app. Ideally, the modified file would be overwritting the initial file in the .ctf package.