You can kill the Silver Hand without activating the power, unless you're on a quest that's different. I've done the next few quests after the transformation, and killed loads of them without using the power.

But all those powers should really work exactly the same as the dragon shouts, just with a longer cooldown before you can use them again. I'm a high elf with a Highborn power that increases magicka regeneration and can be used once per day. To use it, I select it in the menu and then press my dragon shout button.