Will a 1080p signal work on a 1080i tv will it downconvert?

1080p signal may not work on a 1080i TV set. You may not get a picture, but just a blank screen. And that blank screen will not let you undo the changes because you cannot see anything on the screen. In this case, you may have to make an analog connection, such as a composite video connection, to your TV set just to undo the changes you have made. Or you have to press a combination of buttons on the 1080p signal source to restore the picture. I suggest you read the documentation that came with your 1080p signal source.