Here is some info.
The following name change requests must be in writing and require legal documentation
* Change to a first name
* Abbreviate first name to initial
* Prefix change which alters gender (Mr. John Jones to Mrs. John Jones)
* Change which alters relationship (John Jones, Sr. to John Jones, Jr.)
* Send your request along with the proper legal documentation to the American Airlines AAdvantage Department at the address below
* Changes to last name are allowed for life events only - such as marriage or divorce. AAdvantage members who request a last name change for any other reason will be required to submit written legal documentation.