It really depends on how the game does things. Sometimes you get lucky and the game uses a width table with all the values set to the same thing for a "fixed width" font. If the font is truly fixed width, the easiest hack is usually a half-width font. So if it's 16 wide, making it 8 wide. Again, it depends on how the game does things. If it's drawing to a tile-based background, a VWF will be harder than if it's using a separate sprite to display each character. It will require an ASM hack unless there is already a width table in the game. The good news is that a HWF is a great starter ASM hack, and usually easy to turn into a VWF.