The idea behind this is that we encourage audio editing through Audacity but doing so requires
A workflow like this:
after importing a sound in pencil2d:

• open Audacity
• selecting the file to edit,
• Edit stuff or whatever...
• export audio
• maximize pencil2d again
• Select old audio track
• delete audio track
• Import the new audio file

phew... and we're done! Now that was easy right? now you just gotta do that for the 20 or so other tracks you've imported
Well I think that we can do better!

My proposal goes like this: Check if Audacity is installed (should be possible to find and select the executable from properties in case of custom location) then whenever you want to edit an audio file, simply double-click on the track in the timeline. This launches Audacity and starts a new project where you can edit the sound.

Because we obviously can't see what audacity is doing, we'd have to expect that the user overwrites his old audio track, then when Pencil is focused again, the timeline will reload, changing the old audio file with the new.

This makes the workflow look like:

• double-click on audio frame in timeline
  • Automatically launches Audacity
• Edit stuff or whatever...
• export audio
• maximize pencil2d again

Now every time you want to modify an imported sound file, you simply double-click on one of the audio frames which launches audacity, then you can edit, export and BAM the timeline is updated.

The way to check whether the file has been modified could be by checking the file modification date, if it's different, re-import the audio file from it's original path.

How do we launch Audacity and open a project?
Fortunately Audacity has a command-line interface, so doing something like:

$> audacity myAwesometrack.mp3

should launch Audacity, open a project and import the file into that project for you to edit.

While this is of course not better than a built-in audio editing interface, it certainly makes the multi app workflow seem less daunting.