Editing /system/config/adobeviewer.cfg doesn't seem to work anymore, as described in this thread:
https://www.mobileread.com/forums/sho...d.php?t=237423
P.S. I just tried it myself, and I have a different problem. The config file isn't automatically changed back, but it is ignored. I ran "strace AdobeViewer.app <path-to-book>" from the command line, and I saw that the config file wasn't even opened. It seems that the app behaves quite differently between firmware versions.