I smoked a joint or two last night for the first time in a pretty long time. Almost close to a year. I'm actually a bit buzzed as I typed this because I just finished the roach.
To answer your question I don't think it would change much. You'll probably still feel the pressure and pain. I mean it may help. I guess depending on the person. My whole philosophy back in the day when I was still able to smoke weed daily was that "Everything is better when you're high" I probably would have ended up smoking a bunch of weed before taking the route of hanging which was my original method.
Nowadays because of the mental issues that I'm dealing with whenever I smoke weed it just doesn't give me the same feeling that it used to. It can and usually does trigger severe anxiety and panic in me. With that being said I'd rather not take any substances during the process of CTB. Unless I had a gun and got drunk enough to shoot myself.
I was planning on huffing air duster whenever I drop into the noose though. (When it was still my method) I wouldn't recommend anyone doing this I'm not encouraging anyone to take their life I do recommend people to seek out all help and exhaust all options first, I'm just sharing my experiences.