You could change those names over and over again....your letter speaks a universal truth to families of alcoholics.
Is he in an inpatient program? If yes, talk with his counselor about the best time to present this. There are often family groups, or small patient groups, when this letter would be appropriate. Would give him a chance to process. If he's out patient, they don't always have small groups, so I would talk with whomever is running the program.
Your letter is valid. You just want to be sure to present it when he is most ready to hear it. Seek the advise of those professionals who are helping him recover.