Likely no. And if they do, it will cost you. Builders have to submit the structural plans to the city and county before they can begin construction. If they need to make a modification (such as finishing the basement), they will need to go back through the permitting process which can take a long time. If you are hoping to make a change cosmetically (changing the tile, flooring, etc.), they will likely do this – but it will cost. All the elements of the home are ordered very early in the process and making any changes will likely be expensive.