- Is there anything bad about skin protectors for laptops?
The only thing i can think of that would be "bad" is if you use one of those "invisible" plastic skin covers like in your first link, you have to use liquid to apply it, and if you use too much, you can damage your screen. However, it should be fine if you're careful. As for the other types of skins, i don't see anything wrong with them. The case might get slightly warm when using the laptop, but should be ok as long as the cpu fan isn't blocked.
- How do i get the stickiness of the silicon protector back on my laptop keyboard protector?
Get out a hair dryer and gently heat it up the side that touches the keys and apply it while still VERY, VERY WARM/ ALMOST HOT to the laptop. You could try getting some fine sand paper and buffing the contact side first with it. The only thing else I can think of is involves adhesive chemicals or hairspray.
- Will a macbook silicone keyboard protector make a macbook over heat?
No, but it may damage the screen. My dad has a macbook pro and the silicone keyboard protector actually indented the screen.