Survival instict is, as the name instinct suggests, something you cannot consciously influence. As by definition:
Any behavior is instinctive if it is performed without being based upon prior experience (that is, in the absence of learning), and is therefore an expression of innate biological factors
Of course, that doesn't make it any easier to try if you know it's gonna kill you.
I have an unsuccessful suicide attempt behind me (don't misunderstand, I didn't even try to jump, the SI was that strong). But at that time I didn't deal enough with my reasons and my situation in general. I acted impulsively.
Today my views have changed. I have intensively dealt with the questions of taking the bus. I thought about it for a long time. And now comes the most important part: I am satisfied with my decision. I will take the bus because it is the best possible option in my situation. That has almost completely taken away my fear of taking it. So I would say if you are sure that this is the best option for you and you are not impulsive, it can dampen the SI a bit.
What about you? You said that you decided to take the bus two months ago. Do you think it's the only option, or are you unsure? Maybe it's a good idea to think everything through again. You are welcome to write to me privately if you like to talk.