ELI5: How is the Wisconsin GOP’s “lame duck legislative coup” legal? How will WISC be involved?

I live in Colorado. In order for our state legislature to do something like this it would require a change to our constitution, which triggers a vote of the people. Is WI's system of checks and balances set up so that it can erode powers granted to each branch w/o a referred measure? Also, can these brazen new laws be challenged in WI supreme court?