You get exactly one checkpoint restore to any part of your past life. When would you choose and why?

2006, I changed my rate (specialty, MOS) in the service to one that I hated but thought would help me advance, it didn't and I left 1 year later. If I hadn't changed I probably would have stayed in and been retired by now.

That sucks. You did what you thought would be good for you at that point.

May of 2012. I wasn't certain I should propose. I did it, she said yes. We've been married 10 years and are beginning the process of divorce. We have two young boys together. If I could take it all back and spare the hurt, both before, and after, I would

Fuck, that's exactly when we started talking about our marriage (and I was already well accomplished in ignoring red flags), and that is exactly what I would like to reverse. Actually, I want to go back even further and spare us both the fate of meeting each other.
- I'm sorry and I had thought that too. I'm my case, I also ignored red flags. I also ignored that I'd tried several times to end it, but listened to counsel of others who convinced me to tough it out and try to work on things. I thought man I'm killing it!
  
  We had our first post marriage blow up in an uncomfortable loud shouting match at our fancy Maui luau.
  
  "We can keep trying"
  
  Even now, while we're trying to work out her plan to leave, and how to tell our 6 year old that we hope that just before his birthday the apartment will become available. The current estimate says 3 days before.
  
  Imagine being 6, at a "party"surrounded by your friends, and how it will feel that your parents both want to be there, and also don't want to both be there when you get home.
  
  But our current situation creates fights. Neither Mom or Dad are getting what they need from each other. I can't help but feel it's a selfish attitude and choice - but it also isn't
  
  If only I'd been more selfish earlier I could've avoided it all

In games, you keep all your knowledge about things that happen after that point. Is this true in the case too?

You start with the knowledge, but it starts fading, and completely fades away after a week or three. It's up to you to store it somewhere and make use of it. After a month you wouldn't even remember you reloaded. Now give me your answer in exactly 100 words.
- Again, essentially the same question, does the person know about this fading? So much hinges on this question. The answer would be completely different.

The obvious answer to me seems set the save spot shortly after birth. Relive and try all the possible permutations over and over again, groundhogging lives until everything is good enough to say "yeah, that was good, let's leave it there."

Seems like a great method of winning the lottery. I'd find a recent drawing (no huge regrets to undo), memorize the numbers and date, go back, buy the ticket, set for life.

If that's not in the spirit of the question, I guess I could change my college major. The one I got hasn't been very useful. Though, if I did that, I probably wouldn't meet many of the people in my life today. I wouldn't choose to do this for that reason.

I could also refrain from telling a certain flame I loved her. That caused a rift.

Awesome answer! 99/100 (one word short of 100). A very level headed answer, and good for you for not having any major regrets.