Switching Unit A and Unit B of my Duplex

[Hunter Peterson]

I own a duplex and I'd like to switch which unit reads Unit A and which reads Unit B so that they read A to B, left to right. Is there any legal record of which unit is which with the city, state, postal service, etc., that would prevent me from literally just switching the physical letters on my doors and mailboxes? None of the utility meters on the side of the property or on the sidewalk read A or B. 

Thanks for the help!