The easiest way to set a global default setting is from within the KOReader application — long press the option you wish to make the default. KOReader will ask you to confirm the new default.

For users who wish to edit config files directly, there are two such files that contain the initial settings for KOReader's behavior and appearance:

• 1. The defaults.lua located at koreader/defaults.lua.
• 2. The cr3.ini located at koreader/data/cr3.ini, especially for EPUB/FB2 documents.

A very few examples (some of these settings are actually available in the UI, too).

Note that configuration changes to the koreader/defaults.lua file will be overridden by nightly releases/OTA updates automatically and without warning. To make configuration changes persist between updates, you need to move your changes into koreader/defaults.custom.lua.

Alternatively, you can lookup or modify these settings from within KOReader, via the Tools > More tools > Advanced settings menu (top menu, in the File Manager). The modifications will be properly (i.e., in defaults.custom.lua) stored on exit.

Of particular interest in there are the various tap zones (DTAP_ZONE_*), as well as the default ranges for the various CRe settings available in the bottom menu (DCREREADER_CONFIG_*).

A (very) few settings, not (yet) available in menus, can be manually added to settings.reader.lua (while KOReader is not running). They are documented at https://github.com/koreader/koreader/issues/2589#issuecomment-323927682