The ones you don't see for 6 months or so, don't worry about. Those that knew you before, well it's better just to show up and be you. No letter is needed. If they ask then maybe tell them, but otherwise keep them guessing. I work with contractors, engineers and architects too. Oddly enough if they did not see me for 6 months they did now know I use to be different. weird how it was. After six months gee no big deal. I did not have one bad experence, but don't generally deal with guys below foremen.
Relax, breath and be you
Beni