Do you have an X11 application that insists on using a font you hate?
Change that easily with fontconfig.
This syntax in your
.fonts.conf will change the response for one font into an answer from another:
<alias> <family>Gentium</family> <prefer> <family>Tex Gyre Pagella</family> </prefer> </alias>
Add as many stanzas as you like; then run
fc-cache and restart your application.