Could this be achieved by using a custom date range then apply that to the report as it will overwrite the date range for the report.
This would probably benefit from some free text explaining that the date range in the calendar had been overwritten to save confusion.
To create the custom date range; go to Components > Date Ranges > Add > name and tag it as required > Select dates (I assume for this example not rolling dates) > add this to your report in workspace!