States can decertify results (thus decertifying the electors sent to the electoral college) and certify audit results (thus certifying Trump electors) and the electoral college can reconvene. Not saying that will happen but there is a path to Trump/Pence replacing Biden/Harris.
No, states cannot do that. The timeline is very specifically called out in the Constituion, what when it is done, it’s done. There are no take-backs