After wresting with a test for #30870, I am not sure we will ever have the full tests I would like.  Anyway, I concluded that the replacement of font_name is a bug.  It did not matter because all pages are created before configuration is read.  If any of font_name, font_bold, or font_size are changed, set_font_sample is called to define a new font and reset the fonts for the samples on both font and hightlight pages.  I checked that this still works.

I convinced myself that the 3.6+ dialog cannot change 'encoding' in userCfg.