I wonder if someone could try this hack for me:
https://www.mobileread.com/forums/sho...123#post709123
It should do the same thing for PRS-600 that worked for PRS-505 - providing user-editable userStyle.css for EPUB books, which can be used for e.g. default fonts or user-selectable margins. Unfortunately, I don't have a PRS-600 myself and have no experience whatsoever with flashing it.