In general, you have to consider multiple effects: * You will be on record in the ATS for reneging on it. That means any other manager or person at the company reviewing your future application(s) will see it. So even if you are BFF with the manager you reneged on, they will see it and are likely to reject you * You have wasted the time of multiple people. The recruiter and the EM. Maybe the EM is your BFF, but they still had to say no to other potential candidates. And they now have to restart the pipeline from scratch. So you have effectively delayed the hire (and associated value they could have created) by roughly a quarter, at least * The people involved may remember your name. It may not matter today, but in 2-3 years, they may all be at different companies where you could try to apply
I had and knew I never will have any intention of getting back to that company. By not burning bridges I'm referring to the people I've befriended, who I may encounter later in life. But that company, I never will.