Yes, you can do that. What you'll miss though, is if there are any files deleted in the upgraded version. To get around that, you'd want to first delete all the files from the svn working copy, then copy the new files in. Missing files can then be assumed to be deleted and added plus modified files will be picked up.
Note that when deleting the files from the working copy, you need to leave directories and their .svn
subdirectories in place. Removing any resultant empty directories after the upgrade is left as an exercise. :)