Hobbyist here. I want to change a midi drum patch from SI-drum kit to Addictive drums 2. When I made that change and opened up the addictive drums 2 window ... it says the trial version expired. I recently upgraded sonar platinum and expected that ad2 would be updated as well as it's on my list in the command center. What to do?

Go to your product page here: https://www.cakewalk.com/My-Account/Products

Keep this page open as it also contains your Addictive Drum 2 product key. Copy the key to your clipboard if necessary.

Click on "XLN Audio Addictive Drums 2 Producer" and then download Addictive Drum 2 Installation Instructions 1.0.0.8.  That should open instructions to install Addictive drums 2 on your PC

Basically you use the XLN Online installer to install Addictive Drum 2.

And I seem to remember I doesn't stick unless you "run as administartor"? or maybe that was Melodyne. 
But as said AD is a seperate install and activation. 

Promidi, Johnny V ... thanks for you're assistance. AD2 is now up and running at my end. Forum's come through as usual.