Currently it is impossible to distinguish finished and unfinished downloads when looking in KTorrent's download directory without checking the KTorrent GUI too. Is there any way to tell KTorrent to put finished files in another directory as the unfinished downloads, or to append something like .part to unfished downloads?

Zaister wrote:Currently it is impossible to distinguish finished and unfinished downloads when looking in KTorrent's download directory without checking the KTorrent GUI too.

ktshell script?

Is there any way to tell KTorrent to put finished files in another directory as the unfinished downloads, or to append something like .part to unfished downloads?

Nope.
But i think there actually are plans for such option in 2.1, though you have to talk with the devs about that.