I am uncertain what Romney would have done differently. Perhaps a few of the Executive Orders would have been left out, but he supports much of the same, just to a slower pace.
I do not believe he would have implemented Obamacare as he has always said it is unconstitutional.
Just because it was constitutional under the MA constitution IN MA does not make it constitutional for the nation.
I know ONE thing "Romney would have done" for certain:
Round about thirty seconds after he'd been sworn in, the entire damn MSM would have launched all out total war on him.
...and continued harping at him, his family and anyone, anyplace who dared speak of him as anything but unworthy to continue in office (or breathing, if you read between the lines).
(If you think that defeating lib politicians is going to cure any problems, you've only got ten percent of the targets in your sights.)