Short answer is you don't have to redo what is done, BidLight will calculate the delta between old files and new files. And use what is already estimated. BidLight will always use the newest model that you export for each project. unless your start from an old estimation that used an old model, or a you load a session that used an old model. Also BidLight offers continuous estimation, which calculates the delta between old estimate/session/model with your new model. therefore if you have the model already estimated and you made minor or major changes in your model, after export you have the option to use continuous estimation (which uses the delta between the old and new model).