It would probably depend on constitutional interpretation as to what a state legislature could do nowadays. South Carolina's legislature picked their electors until 1860 and if they wanted to revert to that an orignialist interpretation of the constitution would support it. One could make an argument that taking the right to vote away after granting it isn't in line with other later amendments or the spirit of the constitution and the justices seem more than capable of picking and choosing to make whatever outcome they want to happen, happen.

All that being said, switching to apportioning electors according to the popular vote winner would make many more people's votes count given that we're realistically waiting on the results of 7 states to decide the upcoming election.

While re-enfranchising far more people, who have 1/300th the voting power of someone in another state.

States are allowed to good things in service of the union.