(warning: this is based on information I vaguely remember from 5 years ago. things might have changed since then)
Try adding a dummy file (
example - blank hitsound) to the song folder (editor > File > Open Song Folder) and resubmit.
Changing the preview point only modifies the .osu file. When uploading the changes, the system only changes to .osu files and triggers a 'partial' submission, which just sends the new .osu files and no further action is done.
You might be able to make the preview point update with what is known as a
full submission. The editor must recognize that there are new files (e.g. custom hitsound files) that to be uploaded in addition to the .osu changes.
Regardless of whether it works, don't forget to remove the extra file(s) when you're done.
