Do states have the right to rewrite electoral college rules?
I dont believe this is at all Constitutional.
They aren't "rewriting electoral college rules"...they are laying out how electors in their state will be chosen, which is a Constitutional power that state legislatures have a monopoly on (and always have). The chosen electors still have to "meet" and cast their votes.
There are already states with different ways of choosing electors. The one I like best is that the electors shall be chosen by congressional district, with their votes going to the majority of voters in each district, and two statewide electors.
States have the right to award their electoral votes in any manner they (the state government) decides.
They could make it strictly a decision of the state legislature and leave it at that, and as the populace does directly elect the state legislature that would be fine.
Any State Legislature's power to appoint Electors any way they choose is absolute.
states have the right to decide how to allocate the electoral votes... which is why some states like Maine, actually can split and apportion them.