Thanks for the feedback and glad it has become useful to you.
Funnily enough something like what you suggest did occur to me when I wrote it. However I chose not to put it into 1.0 to see if anyone felt a need for it first, a bit like the suggestions from Perkin above.
My interim approach was to allow the user to overwrite the default settings, so that gave you one set stored, plus a second temporarily being used.
However I think the addition of the ability to save the settings as a named set would be the more flexible approach. So if you like a particular font/image for your science fiction books versus another combination for romance etc you could configure that up and then just choose from a list on the left side of the dialog.
I'll add it to the list for v1.1. Kovid has kindly made some additions to the API with 0.7.49 to allow me to set font color so I will be adding Perkin's suggestions as well.