This isn’t new. The “jailbreak” firmwares have been around for a couple years.
No, once installed you cannot update the player with factory firmware. Although the players do not do forced updates you’d want to turn off network update notifications to avoid an accidental update.
BTW, the posted link in the article is a dead link.
Also worth noting that if you want to avoid Cinavia detection in your Oppo, just feed it an MKV or M2TS file and Cinavia will be ignored.