Unless it's a specific accent or something about physicality you have to change I am generally not such a conscious actor.

I learned to change my accent in England your accent identifies you very strongly with a class and I did not want to be held back.

In Paris one is always reminded of being a foreigner. If you park your car wrong it is not the fact that it's on the sidewalk that matters but the fact that you speak with an accent.

I remember walking the dog one day I saw a car full of teenage girls and one of them rolled down the window and yelled 'Marc Jacobs!' in a French accent.

Christopher Reeve did such an amazing job that to give him some kind of accent or more bravado would have been wrong. Audiences wouldn't have responded to that either.