For Superman they don’t need to: his origin has changed pretty radically over time. The guy going PD was raised in an orphanage, no Smallville, no Ma or Pa for quite a while. And even then there’s a big difference between the PD Superman and the mainline Superman: the Kents have to be dead to use the PD stuff. Ma and Pa surviving into adulthood is a Byrne thing so DC still has quite a while before they have to shake things up from the Post Crisis template.
Batman though has pretty much had the same origin since the beginning, it was just expanded and fleshed out. Early Batman killed people and then got quite campy, so the PD version of him won’t be recognizable for a while either.
Really despite the characters early stuff going PD, people won’t be able to use the recognizable versions until the 1980s stuff starts going PD. That’s when you get Byrne Superman, Miller Batman, and Perez WW. That’s when DC is really screwed lol.