Well, I was trying not to, but then people seem to be saying it would be better to just use \def. So I'm confused.
In general, the answer is: I wanted to use the keys processing stuff to update a command to handle more than 9 bits of things. So I started with a file which used a mix of \def, \newcommand, \NewDocumentCommand but no expl3 at all. Once I added the keys stuff, obviously I added expl3 syntax to the mix. So I was trying to clean it up slightly by moving more of it to expl3. Hence, originally I asked if there was something expl3-ish to replace \def\lc@awdur#1-#2\@nil{#1}. And @yo'…