The reader is programmed in Lua.
The application is plain text files, you can read and edit them.
The public repository is at:
https://github.com/kai771/kindlepdfv...tor%3A-History
Just fork it and make your desired changes.
The forum for KOreader is at:
https://www.mobileread.com/forums/forumdisplay.php?f=276
Its public repository is at:
https://github.com/koreader/koreader
Its development is four years ahead of Librerator but should be still relatively easy to backport any of its existing features.
And of course is a good source of worked examples in coding.
Enjoy,
and be sure to let us know where your public repository is at.