Thanks 

I'll let you know if I manage to do it.

No I don't have any other reasons. The bandwidth waste is the only reason I wanted this. Some downloads have 400MBs of par2 files. It adds up quickly on the monthly bandwidth cap.

If you don't feel like implementing it, I might try to do it myself sometime. I'm surprised I'm the only one wanting this.

It would be great if URD didn't download unneeded PAR2 files. It could download only the par2 index file and check the number of blocs needed, then download only what is needed to repair the files. Other usenet downloaders (like Ninan) do this but I didn't find a way to do it with URD.