I'm trying to change one of the sounds

[buoyant magnet]

1. Open up the audio editor
2. Search for "Props_Guitar_01.acp" in the Resource Browser, right-click it and click "Override in "whatever your mod is called"
3. Open the .acp

Import your sample and finally drag the sample into one of the banks while holding shift (this will replace the sample already in the bank rather than adding it on top).