One could say that changes in British imperial policy were more important in relation to the American Revolution in that they stimulated preexisting intellectual assumptions.
These assumptions, the most important of which was a belief in the liberty of the individual, had existed in the American colonies right from the start and indeed were the bequest of the original colonists' English heritage. But it wasn't until the British changed their policies that these assumptions became the foundation for a coherent system of ideas that would, in due course, inspire American colonists to take up arms against the mother country.
Over time, the British subjected the Americans to a series of ever more unpopular taxes that were deeply resented because they constituted a threat to another of the colonists' most fundamental assumptions: that there should be no taxation without representation.
As the Americans were not represented in the Westminster Parliament, they believed that it was manifestly unfair that they should be subject to taxation they couldn't change. British intransigence on this issue only served to increase the colonists' anger and greatly strengthened the cause of those growing voices advocating American independence.
The ideas and the intellectual assumptions of the American colonists had always been there, but they would not have had anything like the importance they did had it not been for changes in British colonial policy, especially those deemed an assault on long-standing liberties that, somewhat ironically, were regarded as the heritage of every Englishman.