Can I change the aspect of an mp4 and save it?

[J Tinsby]

Hello,

I changed the color settings on an mp4 file and saved it. I wanted to change the aspect ratio during the 'save' to 4:3 since that was the original aspect. Is it possible to change the aspect ratio when I save the file again? I couldn't seem to find a way to have that happen, except during playback. If it can be done can someone please show me how?

Thank you in advance!