For the record, this method doesn't make your Pokémon shiny. If you used any value larger than 8 (basically from 0x09 to 0xFF), it basically lowers the xor threshold for them to *appear* shiny.
Focus on the 8/65536 part. Now, recall that you've modified an 8. That's what you changed.
So by changing the value away from 8, you're merely increasing the range of Pokémon that would appear shiny in your game (even if they weren't)
So with that same PID, if the mon was transferred/traded away to other unmodified games, they'll continue to be non-shiny.
Here's an example. I got the exact same Gengar, and it appeared shiny in-game, while not being shiny in PKHeX.
(If you have doubts, here's the pk4: 094 - HAUNT - 9B274A7D4DCF.pk4)
Anyhow, this definitely works, and is fun for single player play. Just don't expect the shininess to retain if trading/transferring out.