The number of justices is set by statute. 28 United States Code Section 1 states:
“The Supreme Court of the United States shall consist of a Chief Justice of the United States and eight associate justices, any six of whom shall constitute a quorum.” Citation
Simply change “eight” to whatever number you’d like. This is a statute so it can be changed like any other statute. It does not require a super-majority or approval of the states. A Democratic controlled Legislature and Executive could change this law.
Would this be a proper response to the proposed actions of the Republicans to replace Justice Ginsburg in this Election Year?
In my opinion YES!