I think that you may already be able to edit the level in options.txt. The manual says that “the last-used Auto-Level settings and Reel” are saved there, and I think that those may be what’s happening in the first line of the file.
In the manual, the example file starts with 6 46345 0. That might mean that reel 6 will be loaded on startup, and that the last auto-level is 46345. What that corresponds to, though, I’m not sure. According to my SD card, my last auto-level was 155344 for a relatively quiet source, so maybe that helps with the available range.