This has been asked for before, ...
... but not for a long time. The only reference to it I found in the Feature Suggestion forum is dated 2006.
In the (F8) Toolbar there are various MIDI transform functions (quantize, alter notes, transpose, compress/expand etc).
Can we have a few more? Reverse, Invert, Harmonic Transpose immediately come to mind. The old Voyetra SEQ+ software from the '80s had a bunch of these transforms that could do some really cool things, seems like it would not be too hard to add a bunch to Reason.