I think installing KOReader would let you configure it https://github.com/koreader/koreader/wiki/Installation-on-Ko...

That said I have a 2012 Kobo Mini with the option in stock firmware (and an undocumented "only refresh when I choose to" setting too). Maybe there's a firmware update for yours that would add it?

I dug one of mine out of the cupboard and just checked. There's an option for refresh after every: with options from 1 page to 6 pages. I guess better than I remembered, but that's still not what I was after.

What I really want is for the framebuffer to remember past pixels, so that the blacking out is restricted to only areas where there previously were pixel. I don't really mind noise on where the text was while the page is replaced, it the big areas flashing black needlessly that's distracting.

I might try out this firmware over the holidays though. If I get back into using the kobo as an e-reader, maybe I'll look at the issue myself now that it's open source, if it's not been addressed by someone already.