In case someone else comes across this..
From what I've gathered in continued reading it seems that asar packages weren't intended to do what I wanted to do with them (using them as a single file storage that I can read into within having to unwrap the whole thing). Once an asar is opened and read into, that process locks the asar file until the UI is reloaded or the application is restarted.
This solution seemed like such an elegant way to do what I wanted though so I kept digging. In the end I ended up working out a way to release the lock on the asar. To do so, open the asar in a child window. The lock is bound to the process that opened it. If you open the asar in a child window and then close that child window, it releases the lock on the asar.