To save any changes you made to your design data back to your original XDC constraint
files, select , or click the Save Constraints button 
.
The Save Constraints command saves any changes made to the constraints, debug cores and configuration, and design configuration settings made in the open design. The Vivado IDE attempts to maintain the original file format as much as possible. Additional constraints are added at the end of the file. Changes to existing constraints remain in their original file locations.