The three transposition options in the Edit menu (on a Mac) are, as follows: Transpose Down 1 semitone, Transpose UP 1 semitone, and Transpose # of semitones.

Even when four bars of chords have been selected, for example, all of the transposition options above still transpose the entire song/project (instead of just the chords I chose), which is why I went with my workaround.

So, it looks like the Mac version of BIAB doesn't have the command, which you have described.