The tab is a manual release for the forward latch. If you use the manual frunk release under the glove box, it only releases the rear latch, allowing the hood to open a couple of inches. You then have to push the tab to release the forward latch. It's a safety mechanism to prevent the hood from flying open and blocking the driver's view, similar to many other cars on the market. If you open the frunk via software (either the touchscreen, app, or keyfob), it releases both latches. (The software locks out that function while driving.)
In later versions of the car, Tesla did away with the second latch, and they moved the manual frunk release from the cabin to the wheel well. I suppose they figure no one will accidentally pull the cord in the wheel well while driving.
So if you remove the tab, I'm not sure what you need to do to get into the frunk in a power outage.