When installing a new or replacement lock, be sure the keyway is positioned so that the cuts of the key will be inserted upward. This will reduce the chance of dirt, dust, and water (which can turn to ice in cold weather) settling in the lock mechanism creating a lockout or stiff operation of the cylinder.
It is always a temptation to take short cuts. You may choose to paint over wallpaper either because you don’t want to take the time to remove it, or perhaps the paper hides cracks and defects in the walls of your older home. Most professionals will suggest that you remove the paper because it may peel or the wall covering texture will be difficult to paint over.