Workaround:
Backup your subscriptions, Delete the subscriptions from MessageStats Reports, then restore your backed up subscriptions.
You will then be able to modify the subscription properties.
T
o back up and Delete Subscriptions:
1. Open MessageStats Reports.
2. Select File | Subscriptions...
3. Select the desired Subscriptions to back up. (CTRL + Click will allow you to select multiple subscriptions)
4. Select Subscriptions | Export selected Subscriptions.
5. Save the file to a location where it would be backed up to.
6. Once all subscriptions are backed up, Select File | Subscriptions...
7. Select the desired Subscriptions to Delete
8. Click the Remove Button.
To Restore your backed up Subscriptions
1. Open MessageStats Reports.
2. Select File | Subscriptions...
3. Select Subscriptions | Import Subscriptions and select the files that were backed up in step 5 above.
This will recreate all your subscriptions and allow you to properly modify the properties.