I do not believe formulatically you can do this back and forth in the same string (...maybe in .NET but I do not use that). What you can do is create a text box and insert different formula fields and apply a different font to each of those. You can make your formula fields return balnks when you want to suppress that portion of the string.
So you break this ....
if {Qdefs.QF1} = "YES" then
Chr(168)+Chr(168)
Else
"__________"
....
into 2 portions.
Formula1=
if {Qdefs.QF1} = "YES" then
Chr(168)+Chr(168)
Formula 2 //
if {Qdefs.QF1} <> "YES" then
"__________"
Make a Text String.
Drag and Drop Formula 1 into it and apply WINGDINGS to just that part of it (not the whole text string).
Drag formula 2 into it and apply ARIAL to that part only.