All you have to do, to extend your trial period, is change number in TrialKey element in application.xml. This file is located in /Library/Application Support/Adobe/Adobe Photoshop/AMT. You can navigate there with this command:
cd /Library/Application\ Support/Adobe/Adobe\ Photoshop\ */AMT
Then you have to open the file and edit it. You can use just TextEdit app.
open -a TextEdit application.xml