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iFixit Tears Down McDonald's McFlurry Machine, Petitions Government for Right to Hack Them
(www.404media.co)
This is a most excellent place for technology news and articles.
https://www.etymonline.com/word/hack#etymonline_v_41496
I don't see anything about hacking in this sense that predates the 1970s. Pretty sure systems hacking predates "IKEA hack" as well.
Earliest I've heard was from MIT and the pranks they do. I think that was from the fifties.
Yes, Ikea hacks are much later. Me and my wife were doing it/calling it that around 2005 when we modded a desk. It was intended to be an example of the dual usage of the word hack.