Not knowing any better I would guess that releasing a healthy wild garter back into the wild would not be a problem. I kept a large female eastern all summer, and she became very “friendly”. She would come to me and crawl onto my hand whenever I would open the viv, and would eat from my hand, no problem. She even let me handle her any time and I never got musked, not even once. I releaser her back into the yard where I found her after she had her babies. About two days later she was out sunning and I thought I would see if she how she would react to me. As soon as I got close, she was gone, just as if I had never kept her. What is my point? I’m not really sure that you can “tame” a snake, at least not like a dog or a cat (maybe not a cat) or horse or even a pig. I think they react on instinct making a return to the natural state much easier. Anyway she was probably just looking for an escape rout when she crawled up on my hand. It’s 20F out tonight and snowing, hope she is snug in a hole under the pool heater or the sunroom floor.
Sometimes I get a little melancholy when winter arrives.