I realise my initial question was somewhat generalised - I was wary of being too wordy! The kind of editing I'm referring to can best be illustrated by a few hypothetical examples:
Example 1: I've recorded a piano performance, but there's one particular range of notes (let's say C5 - A5) that sounds unpleasant above a velocity of 110. If any notes in that range exceeds 110, I want to reduce them (and only them) to exactly 110.
Example 2: I have some sampled strings - their volume is controlled by MIDI CC7. I've drawn a series of intricate CC7 controller curves to control their dynamics - its shape is just right. Now I change my mind - I don't like those strings and change them for a different string library - but its dynamics are controlled by CC1, not CC7. I want to transform the CC7 curve I spent ages getting right into CC1.
Example 3: I've programmed a marching snare rhythm. The actual part is what I want, but the velocity range of what I've played is too wide. I decide the best sounding velocity range of the snare is between 30 and 70. I want to compress the recorded velocities, and centre the result around velocity 50.
These only a few examples of editing tasks that are very hard to do in Studio One, and some would appear to be impossible -but they're the kind of thing I do all the time. In Sonar (my current DAW) the above examples can all be done quickly with a handful of clicks using either the Interpolate feature or CAL scripts.
I know Sonar's way of doing things isn't everyone's cup of tea, but it is capable of doing most MIDI transform functions very easily. So why don't I stick with Sonar, you may ask? Because I love everything else about Studio One, and would jump ship happily if only I could do the same sort of MIDI manipulations that I can in Sonar.