I read a forum article indicating that uploading cannot be stopped while downloading. I know why this question has been asked. When using a VPN, your url address is masked, however, when uploading, your url is available to all who wish to cause problems. If you can recommend a way to block the originating url when uploading, this would be great. I have had too many problems with watchdog groups.
You can set upload to a ridiculously low level but if you stop it completely, downloads stop working as the seeder needs packets to be acknowledged.
You could try disabling long term seeding and stop any downloaded files.
However, that sort of negates the whole purpose where it's file SHARING.
You could also run a VPN to hide your IP address