I only put this on because I didn't realize it, a couple of people who have already hit 60 didn't realize it, and I don't know of anyone else who did.
Hit Escape > Options > Gameplay > Interface on the bottom is the option for Elective Mode
Check the box next to Elective Mode. Apply and Accept.
Congratulations! You are now unrestricted in the abilities that you place in your toolbar. You may have multiple abilities from the same tree in your toolbar!
Place your desired abilities in the toolbar, remember you can now place any ability in the toolbar you want!
For Example, as a Monk (because everybody has a monk) you could have your Blinding Flash and Breath of Heaven both tasked on at the same time. What's that? They're both part of the Defensive tree? Who cares? YOU'RE IN ELECTIVE MODE!
Disclaimer: I am not responsible for the after-effects of having your mind-blown, nor the destruction, ownage, mayhem, chaos, and/or violence caused by your new combination possibilities. However, if you want to send me gifts for sharing this knowledge, please do. Seriously, give me shit.
________________________________ 1st Marine Raider Battalion