I couldn't get packer.c to work right, so I think it outputs to stdout.txt. Just copy all of the text in it into font.h and it shoud work. You might also need to copy the new font.bin into /font if it's not already there.

editor.exe automatically saves font.bin when you draw. Also, don't edit A0, that is actually used by the powder toy. Press + (=) and - to scroll right until you get to a bunch of thermometers in a row, and edit the first one of those.