As in a VC game? No. Unless you extract the ROM, hack the ROM (dunno if there are ROM hacking tools for NES or whatever that game was on. probably are.), pack it back into VC channel and reinstall. Seems ever so slightly excessive.
You can set the Homebrew Channel to use a different font (like in my theme here: http://www.wiibrew.o...ttingsTheme.png ). Just add the font and the following lines to the "theme.xml" file: