Although it is possible to overwrite a previously saved baseline, care should be taken before doing so. The nature of a baseline is that it is something that should remain static and unchanged. Consider saving an additional baseline instead of overwriting. Overwriting a baseline will save the current state of the Start, Finish, Work, Duration, and Cost fields into the Baseline fields.
Overwriting a Baseline
Click the Tools, Tracking, Save Baseline menu item.
Select the baseline you want to overwrite.
If it has already been saved, a date will be shown.