New sub here after seeing it on fedigrow.
I do interstitial journaling as part of my PKM.
To answer the questions:
Would I? Even tough my mind feels a resolute "nope!", I would say yes, such power would just be too much to not use. (Or try). I would put small experiments first to see what can, and what the consequences are of changing the past.
What would I change? I would try to alter small events that caused me great grief later on but not the big things. I feel those have made me who I am, good or bad.
What I'd rather try to do is change the timeline to skip certain parts, like fast-forwarding in a movie. Go from my ex-gf to my now wife (without the rebounds and akward flirtings).
Change which friends I would meet sooner, so I'd have more time with them. Knowing friends come and go, the ones who stay.. I wish I could add years to those friendships.
Also change little habits that would improve my health down the line so I can live longer.
And maybe I would try to change my career, so I could have started where I am now but younger so I didn't burn-out on an ex-job. I do feel the burn-out forged me, so I might leave that in.
Tl; dr i'd change nothing big, just adjust the timeline and leave out everything that didn't change or add value to me as a person. (In a way I would Marie Kondo my past but keeling everything that made me feel, and dropping everything I'm indifferent for.)