I would like it a lot if BB and RB treated the add2 and add9 differently. Especially useful when it comes to guitar fingerpicking backing tracks. I've used two workarounds:
1) adding higher accents by recording a second guitar track directly into RB (MIDI or Audio) to match my desired flavor (usually higher add9s)
2) creating a duplicate BB-generated guitar MIDI track (could be any instrument)in RB, shifting the MIDI notes up an octave, then killing all the unnecessary notes in the duplicate track, then assigning a guitar VSTi/VST. I typically use Sforzando and Ample Martin Lite and they work well. Both are okay for these kinds of add9 accents covering a few measures. Not so great for entire backing tracks. Still, very doable... if you're retired, happily housebound, given special permission to stay in the studio longer while putting other things on the back burner, etc. Dare to dream on.

Songwriter, not Singer-Songwriter. Dropped singing in time to save a few friends and pets. Website: www.songmaker.ca