Hey there, I finally added a tool to export and import sounds for characters and other things for the sound files found in the game's folder: Media\Sounds\SE\
How to import custom sounds:
In the Mod Tool, open a sound file such as: Media\Sounds\SE\pv_boog.dat
Go to the "Sound Editor" tab and click "Export all as .wav" and choose a folder where the .wav sound files will be exported.
You can use Audacity (free) to record, edit and save sound files.
The custom audio files need to be saved as .wav with the encoding: Signed 16 Bit PCM
Also the audio must be mono, if you have two tracks(stereo), to turn it into mono, in audacity right click on the left of the audio track and click "Split stereo to mono" then delete the second bottom track by clicking on the [x]
To save a file as such in Audacity, go to File > Export > Export as WAV
Then in the Export Audio window, in Encoding, select "Signed 16-bit PCM" and save.
When importing custom sounds, the wav files should be named as how the Mod Tool names them when exporting all the sounds of the .dat file (with "Export all as .wav"), so for instance with pv_boog.dat the sound files are exported as "pv_boog_1.wav" "pv_boog_2.wav" "pv_boog_3.wav" etc and you should keep those names for importing.