geeze, I was afraid that wonderful degree of control was taken out to get it running on a reader. Thanks for letting me know.
To be honest about the only reason I like FBReader is because of the amazing degree of control it offers on other platforms. And your typical user is, well, not going to be able to find and modify the style.xml file. Now it brings up the question, what changes were made to the styles/config controls exposed. I mean it could be that those to properties are simply not there to be set by the user which could explain why they don't work.
I did some checking on my Windows version of FBReader and the changes I made were not saved to the styles.xml file. I am not sure where they are saved but that could be why you can't make it happen if you are adding the changes to the original styles.xml. Then again if you do make changes there, sans an over-riding entry in whatever custom "styles.xml" file, then it "should" make changes to the default look and feel of FBR.
I am sort of out of it tonight as I had to take one of my stronger meds tonight, but if I can find more I'll post it for ya to try. BTW, as for me knowing where stuff is stored on a Linux device...the last time I managed a -ix network was in 1991-1993 and I've kept away from it ever since...long painful story.