I am not sure about iPhones but opened all of my Macs before, sometimes to do some upgrades or clean up. It never voided warranty. All three had some work done by Apple. As long as you do not screw up yourself something during repair, it is fine.
I would expect majority of HN population to be able to follow step by step guides online.
I would expect majority of HN population to be able to follow step by step guides online.