ToTTeR will create three macros for your rogue which you can place on your action bar. One for main tank, one for off tank, and one for a rogue.
You can then bind any three keys on your keyboard as keys which will "assign" a player into the corresponding macro.
Once set up you can simply click the player you would like to assign as the main tank and then press the "assign" key for main tank. And so on for off tank and a rogue.
Now you can cast tricks of the trade on any of the three targets at any time throughout the raid without having to switch targets!
1. Download and extract to your interface/addons folder
2. Log in to your rogue
3. Open your key bindings and give bindings to 'assign MT', 'assign OT', and 'assign Rogue' under 'ToTTeR'
4. Open your macros frame and drag the new macros onto your action bar
Now you're all set. Just click a player you'd like to assign as your target for the macros and press your chosen key.