The Requant.exe program will take an oversized media file ( file name following the -i paramter) and shrink it by a specified amount ( "-level 96.14" in this example) and give you a reduced size file ( -o xxxxxx). Clearly you have to calculate the reduction % yourself.
You would create a command file in notepad substituting the real locations & filenames & then run that command file from the command prompt.
I've never done this as it's automatic with the D2SRoba front end.

Personally I always use the D2SRoba front end to DVD2SVCD. I also use Cinema Craft encoder which you'd usually do a 3 or 4 pass process with but the D2SRoba does sampling to work out vbr rates & stuff & does just a single pass. I've not found any quality differences but processing is way faster.

The Film Machine would work in very much the same way as you're doing now & could require that you shrink after the video has been compiled.