HMSetFont
HMSetFont Set the font used to display text in help balloons
#include <Balloons.h> Help Manager
short font; the global font number
You can use the HMSetFont function to set the font that is currently
used to display text in help balloons.
font: specifies the global font number for the Help Manager to use to
display text in help balloons. This sets the font for help balloons in
all applications and software that display help balloons. Use this
function with extreme restraint; the default font provides a
consistent look across applications.
Returns: an Error Code.
noErr (0) No error
memFullErr (-108) Not enough room in heap zone

Warning: If your application changes the font name or size, the change affects
all applications and software that display help balloons