Rewrite 'Tempus, Anyone?' so that Alt-Clark's secret identity as Superman isn't revealed on television (or at all), but still have it end with canon Lois returning to her Clark.
Now, go a step further. How does alt-Clark's life change, being able keep his Superman and Clark personas separate? Does he reconcile with Lana and live happily ever after with her? Does he go in search of his alt-Lois? Does he move on as a single Clark and search for love elsewhere? (cough, cough, alt-Mayson perhaps.
) What happens to Alt-Clark with this one change?
Keep in mind that whether or not he's out as Superman in his home dimension doesn't affect his coming to help canon dimension during the Doe arc.