You should be able to do that. If you suppress the Home key as well, you could create a profile for it that disables key suppression, then your volume buttons would work as normal. I'm not sure about suppressing the power button; I don't have my tablet with me at the moment to check. Just scroll through the list of keys in AutoInput to see if there's an entry for it.
The tasks that I described won't stay running. It's more like flipping a switch; they do their job and just exit. That's why you need two tasks; one to turn it on and one to turn it off.
However, for other purposes Tasker does have a "Stop Task" action that you can use to kill a long-running task. I believe it's in the "Task" section of the action list. You just need to supply the name of the task you want to kill. For best results, the task you are trying to kill should be running at a lower priority than the one doing the killing.