[Ripplinger]

I've used Boroda's CFW in the past when PRS+ required it, but now PRS+ stands on its own and is self-installing and is really very nice. You can have as many custom stylesheets as you want for various fonts and can change them on the fly from Settings > PRS+ Settings > Book Viewer Settings > User EPUB Style (CSS Files), and then you have your list of files you've installed (I've included a screenshot of my list as an example, being able to take screenshots like this are part of PRS+). Simply select which one you want to use from the list. You just have to swap books by opening a different one, then go back to the one you had before to force the font change.

And both Arno and Palatino worked for me. I only used 4 from each font pack for normal and bold in regular and italic, and have screenshots of each plus default in small font. The font style differences are much more noticeable in medium font size though. The fonts I used were ARNOPRO-REGULAR.OTF, ARNOPRO-BOLD.OTF, ARNOPRO-ITALIC.OTF, ARNOPRO-BOLDITALIC.OTF, and PALATINOLTSTD-MEDIUM.OTF, PALATINOLTSTD-BOLD.OTF, PALATINOLTSTD-MEDIUMITALIC.OTF, PALATINOLTSTD-BOLDITALIC.OTF. I didn't rename them at all and they worked fine.

And I'll have to try adding !important to the css files and see if that really will overwrite those epubs that specify their own font. I always find those most annoying since I prefer LexiaDaMa still (including a sample of that font too just for comparison).

Edit: Btw, my reader viewing settings are at 127/-125, I didn't think to change that back to default before taking the screenshots, so they probably look more saturated than you're used to.