Would putting a tool in the oven at 275° for an hour ruin the metal?

Here you have to put the degree designator, which is F for the polymer clay you are talking about. If it were 275C it would probably still work without ruining the metal. But your project is probably not going to work because polymer (oven baked) clay shrinks while baking and will probably crack off the handles.
You need to use Tool Dip which is a soft plastic air dry/cure for the purpose you name. https://www.google.com/search?q=Tool+dip+&ie=utf-8&oe=utf-8

275F DOES NOT ABLE TO HARM ANY COMMON METAL THAT WE HAVE IN HOUSE.

Actually, it probably will change the temper but the real question is does it matter? It shouldn't ~dramatically~ change it, but it's pretty darn close to tempering temperature and the fact that it's an hour matters a lot. Anytime you heat steel it tinkers with the structure of it, one way or another. My good pliers are $60 and I wouldn't even consider what you say with those. If you are talking about $10 hardware store pliers then it doesn't mean so much and it's worth a shot.

°C or °F? If °C, you may alter the temper of the material. If °F, probably won't affect the material.