There are lots of radical changes that could be made in the law and politics that would not involve any constitutional change, and likewise, there are many constitutional changes that are trivial in terms of their impact.
Ireland recently narrowly defeated a referendum to abolish the upper house in its legislature. Institutionally, it was a big change. But, in terms of practical impact on the average Irishman, it was a low salience matter that was almost irrelevant.
In the United States, a moderate legislative tweak to the Posse Comitatus Act (18 U.S.C. Section 1385), could profoundly change the very nature of American political life by giving the (highly politically popular) active duty military a greater role in law enforcement, via a mere act of Congress. Few bills are better examples of the "unwritten constitution" component of the American constitutional order in a broad sense.
Some principles of law that are time honored and the focus of immense law school study and litigation consideration, like the parole evidence rule of contract law, turn out to have negligible impact on the day to day functioning of the legal system in places like Israel that have abolished it.
This isn't to say that the content of the U.S. Constitution, substantive laws or national policies don't matter. You need only look at the often vast differences between life on opposite sides of international borders such as the U.S.-Mexico border, or the Germany-France border to see that this is the case. But, the pressure points of policies that matter aren't at all obvious and are frequently not very accurately know by even academic experts who often lean heavily on conventional wisdom and institutional myth and logical reasoning, rather than empirical reality in making their assessments. Practitioners, lobbyists, middle managers in bureaucracies that implement these policies, and small business people who deal with these laws personally on a day to day basis tend to be much better informed about what would really matter and what would not.
There are also tipping points. Take election law. A lot of election law and process details have only incremental impact, any of which can determine the outcome of a close election. And, the basis constitutional election structure mostly influences how many political parties will have elected representatives and the likelihood that coalition government will be necessary. But, pretty much any system that makes it easier and more reliable for an opposition to organize an election campaign to oust the current regime than engaging in an armed insurgency or carrying out a coup in cases that aren't close is enough to meet the basic requirements of democratic government.
If one is to really have a good practical ability to shape policy, figuring out where the pressure points are and which are most malleable is the name of the game.