It is possible. You used to be able to get VHS videos which allowed you to dub onto one of the stereo tracks with music or commentary after you had transferred your camcorder material, but I don't know if they still make them.
The more conventional way is to use a sound mixer like this one here;
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. Basically you would attatch the audio cables from your camcorder, and a microphone and a CD player into the mixer, which combines all the audio inputs to just two channels, and then attach cables from the mixer to your VHS. This would allow you to add music or voice whilst copying your material.
This method though is imprecise and outdated, I would recommend going the digital route, and doing it on your computer (If it's powerful enough). There are loads of packages like Adobe Premiere, which will not only allow you to add voiceover and music, but also to edit your material into a more watchable form.