My first thought was to use imagemagick, which I've used for similar tasks in the past, but it does not seem to output svg files very nicely.
Eventually I found a program called rsvg-convert, which worked quite well. I believe it is also possible, perhaps even simple, to resize svg images by directly editing the xml text in the svg file, but I did not have the patience to do read the file specification and figure out how to do that.
I'm on ubuntu, so I installed rsvg-convert with apt-get:
sudo apt-get install librsvg2-bin
I created a directory, copied all of the svg files I wanted to modify into that directory, created a subdirectory for the new files, then created resize.sh in the subdirectory and executed it from there.
for i in `ls .. | grep svg` do rsvg-convert -f svg ../$i -w 50 -a -o $i done
(someone here suggests to use rsvg-convert, but doesn't go into any more detail)