The new bill ostensibly includes changes to address problems with the original, like giving local elected officials a tiny bit more input in what happens to their cities and towns. But the real difference may be that Republicans attached an appropriation to this bill so that it won't be subject to referendum.
Michigan Republicans have an ... interesting relationship with ballot measures their state's voters voted on in November. One of the big lines Republicans are trying to sell to explain why they decided to attack unions during the lame duck session is that it's retribution for unions putting a collective bargaining measure on the ballot in November. Republicans just had to weaken unions because unions had the temerity to try to strengthen themselves, or something. Never mind that this is contradicted by the fact that some Republicans in the legislature, and of course a bunch of big donors and far-right think tanks, had been working on their anti-union bill since well before the collective bargaining ballot measure was proposed. Never mind that the timing is obvious: pushing such a divisive law before the election would have had repercussions for Republicans in November, and with the state House gaining Democrats come January, it was now or never. No, we're supposed to believe that a failed ballot measure forced their hand. But at the same time, we're supposed to believe that the successful ballot measure repealing Public Act 4 was also a legitimate reason to pass virtually the same law, with some cosmetic changes and an appropriation.
In other words, to Michigan Republicans, democracy is just something to override, evade, or blame.