Yes, files in your app's sandbox are kept during an update. Though it is possible that files in the Library/Caches
folder could be purged.
Keep in mind that the value for XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX
will change during an update.
If you are keeping a reference to a file, be sure you only store a relative reference and not an absolute reference.
For example, if you know you are storing files in the Documents
folder, just keep a reference relative to the Documents
folder. At runtime you can get the path to the Documents
folder and then append your relative path.