Change of Name and Religion

One of my Hindu friends by name Narayan has embraced Islam and as per requirement of the procedure he has been named as Rizwan. He does not wish to change his name in all his previous documents(educational certificates, passports, etc) and wants to continue the same in the name of Narayan only. He will be marrying a Muslim girl as "RIZWAN". Therefore, he would like to make an affidavit with the above details and state that "NARAYAN IS ALSO KNOWN AS RIZWAN". Will the above affidavit be valid and serve the purpose of "Supporting Document" for all his previous documents and for all his and his spouse's future requirements? Please Advise.