Modify User Name label

Is it possible to change the label "User Name" on the Registration form to something like "SCMA Account#"   ?

Our setup requires the user to use his internal account number (which is unique) as his user name - yet they continually try to put in "JohnDoe"...we have verbiage above the webpart explaining this-but it would be nice to be able to re-label that field.

Yes - just edit the web part settings.  All of the labels, error messages etc... are stored as properties and can be changed.