[wizzwizz4]

That's subjective. Objectively, all we can say is that it happened before 2017.

[gerad]

No it’s relative. ;)

[pavel_lishin]

Well, it certainly didn't happen tomorrow.

[exe34]

in some reference frames, yes.

[wizzwizz4]

No, not if we've observed it. There are predicted historical events which can be shunted into the future by running away bravely, but if you've seen them happen, you can only change how long ago.

[exe34]

not for us, but in some other reference frame.

[wizzwizz4]

If by "reference frame" you mean "observer who lives in the past", then yes: the past is sometimes the future of a more distant past.