I did last year, but I moved and now live where I don't get any trick-or-treaters. I used Ryuu, my BCI, but he was only about 3.5 feet at the time. He was very good for it. We didn't have a whole bunch (only about a dozen total), so I sat on the couch and watched TV with him until someone knocked, then got him draped over my shoulders. It seemed like most of the time they didn't even notice him! I didn't flaunt him and wasn't dressed up, just had on a shirt that says "Witch and Famous"
The ones that did see him usually said "Cool! Is that real?" and at that point I'd say "yes, would you like to pet him?" as I crouched down and offered the tail end. They all did, including a couple parents that would come up closer to do so.
My favourite was a little boy about 8 who hadn't seen him. He said thank you and turned to go, and his dad asked him if he saw the snake. He turned around and saw him and said "awesome, can I pet him?" I let him pet him, he said thanks again, and went down the steps. As they left I heard him say "Can we get a snake?".I shut the door and started laughing! That made my night!
I think in general, unless you're nervous about people knowing that you own snakes, and you're not purposely using it as a prop to SCARE, that it's fine to do. People are expecting to be scared so it's not like it's a shock when you answer the door. Much better than someone with a mask jumping out.