for your first question; if you move the product from your temp category to an active category, the product is not automatically turned on. (you have to click the red button to turn it green again) So as long as the product itself is set to 'not active' you can do all the updating you want and it wont tell twitter until it is active (green button in the category)

2nd question: once you activate the new category and the products within twitter will not be notified (as with both scenarios) until you actually click on a specific product and update it.