We are updating user names from say X to Y. Will following Change?

Summary: We are updating user names from say X to Y. Earlier the user names were like John.Davis@domain.com, now we are replacing it with DAVISJOHN

Will following work or do we need to create new?

a) Existing scheduled Reports with John.Davis@domain.com.

b) Data Access

Content (please ensure you mask any confidential information):na

Version (include the version you are using, if applicable):26C

Code Snippet (add any code snippets that support your topic, if applicable):na