I was worried that Tom Graham was lonely here, so I'm bringing my best idea to the forum:
While in Preview mode, Pro Tools should restrict playback of the changed automation parameters to the selection only. If no selection has been made, Preview would function the usual way. With a selection, the underlying automation would play during pre-roll, then switch to the Preview automation, and switch out during post-roll.
I was with a client today, auditioning a tweak to one line of dialog, and it was impossible to really get a sense of how the tweak would sound in context without hitting suspend preview on the fly.
For the pro mixers out there, would this help you? Any drawbacks?
Yes,
it's on Ideascale.