If it's just a singed ear, it's okay. Some snakes do find the smell of singed fur off-putting. But it's definitely not enough by itself to trigger regurgitation. I've been feeding a dozen animals f/t for several years in a row, and burned ears just aren't a big deal.

But you do want to make sure you didn't cook the mouse whenever you remove it from under the heat lamp. To be safe: take the mouse and wrap you hand around it. If you can FEEL the heat through your palm, and your brain says: "man, that's a pizza burn waiting to happen", then yeah, you've cooked the mouse. At the bare minimum, you'll be cleaning up exploded mouse guts if you feed that rodent to a snake. If it feels like cooked meat in your hand: THROW IT OUT.