You can't change the names of any fields, user-defined or built-in. You can,
however, change the label text on a custom form page.

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Sue Mosher, Outlook MVP
Author of
Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> For example i would like to change the field 'Birthday' in activities to
> 'Renewal date'