When trying to save modifications in the Rule an error is displayed stating Unable to save changes
One of the basic troubleshooting steps is to try the same steps using a different browser to verify it is not a browser specific issue. Typically Firefox and Chrome works much better than IE.
As a best practice it is recommended not to modify out of the box Rules but instead make a copy of the Rule/s that need to be modifies and make changes to the copied Rule/s. Then disable the original rule/s.