Origin seed is reverse calculated based from a bunch of factors relating to RNG.
As such, you can't just "modify origin seed" directly. And to answer to your nowadays portion, that isn't accurate. As far as I can tell, one has never been able to edit it directly.
You wanna change your origin seed, you can do so indirectly: change every other stat relating to that chain of RNG frames [stats the can be reverse calculated to determine the PID Method used]. (PID, IVs etc)
Also, just a neat bit of info for ya: hovering isn't the only way to see origin seed. You can control click on the (!); origin seed is in the full legality report.