Board replacement is a process that we do when there are stains in the floor that don't sand out or if boards are damaged by some other means.  What we do in board replacement is to cut out the affected boards and replace them with new ones.  We do not have to replace whole sections of flooring, only the boards that are affected.  Once the replacement is done, in most cases you will not be able to notice that is was done except when the floors are very aged, then there may be a slight color difference.