Of course you can "change the past" ... except you already did
https://www.scribd.com/document/503128860/Larry-Niven-THE-TH...
In some of them (like that Heinlein story) there is just one timeline and you at best get causal knots, in others (like Asimov’s End of Eternity) a time traveller experiences different timelines and whatever other experience is ‘undefined behavior’
I don’t think Nicen wrote stories about traveling into the past but plenty about traveling into the future with cold sleep, stasis boxes, and relativistic travel with Bussard Ramjets, I guess you could have done it even more stylishly if you could afford to buy the secret of the Outsider reactionless drive.