In the current beta you can only select a single effect for editing. The good news is that selecting multiple effects and editing them is already implemented so look forward to the next beta release.
Thanks Ty. Great to hear that its already implemented in the next beta release. This would be a great help to some of the work we are doing.
Beta II is now available so this feature is now available to you. You can shift-click both effects in the timeline as well as tracks.
Another thing to try is smoothing multiple transitions at once. Try this:
1. In a project with several transition, shift select all the transitions in the timeline.
2. Click the arrow to the right of "Smooth Transition" in the Timeline to control your smoothing option
3. Click "Smooth Transition". This command will smooth all the selected transition.