Unfortunately, it seems some command have templates and some have patterns. For example, if you look at the "drop" command, you'll see:
<command name="drop" template="drop">
whereas for something like "ask" which has a command template, you have:
<command name="ask" pattern="[ask]">
If you change the drop command to be:
<command name="drop" pattern="[drop]">
then
<template templatetype="command" name="drop"><![CDATA[^let (?<object>.*) fall$]]></template>
will work. But you probably don't want to be doing that. That is, assuming you're trying to create a general-purpose language file, you can't be arbitrarily changing the core commands. If it's just for your own work, then you could import the verb into your game and change it locally.
I'll keep looking at it, but I haven't found a way to make it work so far.