How to determine if user making a change is the same user that's being edited?

Summary: How can I determine if someone is changing their own name in Personal Information?

Content (required): Customer - Estes Express Lines; Use Case - 1.

I have written a Field Validation rule for the Person Name business object...to display an error message if the Start Date is not the Current Date when a change is made. I'd like to only perform the check if someone is updating their own name in Personal Information > Personal Details.

Is there a way to tell if the user making the change is the same as the worker who's name is being changed?

Version (include the version you are using, if applicable): We are on 21C...going to 21D tomorrow night.