The filesystem image is the same before and after this commit:
$ sha256sum fox32os-orig.img fox32os.img
abc77bd6310b8eb6bcde0a8a442ca8bab071307a6cf5155ea606578435f77d27 fox32os-orig.img
abc77bd6310b8eb6bcde0a8a442ca8bab071307a6cf5155ea606578435f77d27 fox32os.img
The conversion was performed with a few sed commands:
find -name '*.asm' | xargs sed -i -e 's/data.str \("[^"]*"\) data.8 0$/data.strz \1/g'
find -name '*.asm' | xargs sed -i -e 's/data.str \("[^"]*"\) data.8 0 /data.strz \1 /g'
find -name '*.asm' | xargs sed -i -e 's/data.str \("[^"]*"\) data.8 0x00 /data.strz \1 /g'