Without using Videopad, you can right-click on the clip in the PC folder and EDIT IN WAVEPAD, then import the result to Videopad.
If the clip is already loaded into VP, prior to unlinking there should be a right-click option to EDIT IN WAVEPAD, along with the option to SAVE AS NEW AUDIO FILE - even after unlinking.
The former will launch WP. When closing it the edited clip should be auto-replaced in VP. But save your changes first for protection.
The latter creates a new WAV file that can be imported to WP, edited, then manually imported back into VP. The file is normally stored in your MUSIC folder.