It would be better for them just to treat the series as an Elseworlds story. Or perhaps a different Earth than the main DC universe Earth. They have reestablished the multiverse haven't they?
"Tell my tale to those who ask. Tell it truly, the ill deeds along with the good and let me be judged accordingly. The rest is silence." -- Dinobot
For this to all work...
Perry White must become editor of the Daily Planet
Lex Luthor must re-establish himself as the richest man in Metropolis
Chloe must disappear
Lois must return to Metropolis
Lana, Lois, Perry, Lex, Oliver, Arthur, Impulse, Cyborg, Manhunter, and a few others must have their memories tampered with...
and Clark must leave the Daily Planet and then return, noone remember him.
Oh and Kara has to be kicked off the planet >.> Basically all modern age heroes and villains have to be reset to a degree or our thinking about them has to be fudged...as in by "debuting" we mean that they reveal their existence as "real" to the public in some way and be given a name.
Of course that's just based on what I know of a mishmash of canon from Silver age, Modern age, and reading up on the stuff... so whatever...
Oh Superman must exist by the end of this season and Blue Beetle as seen in the demo, must not as that Blue Beetle is from Infinite Crisis and didn't debut for a long time >.>