On the topic of how to tell Qtractor to reload an audio clip that has been edited in an external program, you might look at how Cakewalk Pro Audio 9 did it. If you edited an audio clip in an external program (Soundforge), as soon as you saved the clip and exited Soundforge, Cakewalk asked if you wanted to reload that audio file. I suppose they used a semaphore of some sort to tell CW that it had changed.
On the topic of how to tell Qtractor to reload an audio clip that has been edited in an external program, you might look at how Cakewalk Pro Audio 9 did it. If you edited an audio clip in an external program (Soundforge), as soon as you saved the clip and exited Soundforge, Cakewalk asked if you wanted to reload that audio file. I suppose they used a semaphore of some sort to tell CW that it had changed.