Setting Keen Galaxy difficulty with Emscripten DOSBox

Today I set up Keen 4 in the Emscriptenified version of DOSBox with the tedlevel parameter supplied so that the game goes straight into the specified level. Unfortunately, using that mode always sets the difficulty to Normal; attempts to change it by starting a new game in the running program just deadlock it. I first figured out how to patch the tedlevel difficulty: it's a word at $3BBE from 1 (easy) to 3 (hard). The patch script uses %patchfile to load a given file at that address. That file, one byte long, is injected into the DOSBox filesystem at page load using FS_createDataFile with the data appropriate for the user's selection.