RealBand does have a RT tempo substitution option.

This is from the RTTempoSwaps file for Vibes...

1215,85=1216,140 ;Vibes, Rhythm Bossa Ev
1219,60=1217,110=1218,140 ;Vibes, Rhythm Jazz Sw
1226,60=1222,110=1224,140 ;Vibes, Soloist Jazz Sw
1227,60=1223,110=1225,140 ;Vibes, Soloist Jazz Sw (Bluesy)

To decipher the last line 1227, 1223, and 1225 are the RT#. 60, 110 and 140 are the tempos for those sets. The range is usually about 10 bpm under the next highest tempo. In other words, the 110 RT will automatically change at around 130 and use the 140 RT. If you load a RT in BIAB and change tempo, you'll see where this happens. Of course, you have to have RT tempo swap enabled which, I think, is the default.

R