I've looked in the documentation and FAQ to see if there's a way to do this - and I don't *think* there is, but apologies if I'm wrong.
Okay, it seems that the only way to record changes to a contraption parameter is to go through this series of steps:
1) Right click on the knob / slider you wish to alter
2) Select automate
3) Record enable the resulting automation lane
4) (if not already done) Enable Automation Recording on the transport toolbar
On some of the VST's I have, I can't always right click (step 1, above) and have to right click on the VST, open parameter control, find the parameter I want to record and the proceed with step 2 and onward.
It would be fantastic to have an option wherein anything I change is automatically sent to an automation lane and recorded. If you're familiar with the old Rebirth stuff from Propellerheads, it's pretty much like that. Anything you changed was instantly recorded without having to set it up initially.