Yes on both. In Motion, select the Project in the Layers List, then in the Inspector you'll see all your published parameters. You simply drag them to change the order.
For the blend mode, just add a checkbox widget and rig it to change the blend mode. Easy-peasy.
Freelance Producer/Editor/Motion Graphics Artist
Apple-certified Master Trainer
Author, Motion 4 from Peachpit Press http://www.applemotion.net