[pk_hat]

If you want the 'tweak' to be in realtime (ie: a slow filter sweep over 2 measures), you need to record that automation in Reason. Just as you would record a musical passage from, say, a synth, record over the area you want to automate, do your tweak, and that's pretty much it. You'll see a green highlight around the parameter you just altered. You can also just right-click (or ctrl+click) on any parameter and select "edit automation", in which case you'll be able to draw the automation in the parameter's window (created automatically and placed below the instrument or effect related to it).

This way of doing it is sometimes more efficient, as it allows you to be more precise with your edit. Once you take care of all this in Reason, you can just route the audio into ProTools and print it to a track.