You could instead say that in the late 1780s France doesn't suffer repeated bad harvests.
You can also just change some policies so that there are a series of reforms but France never gets to a revolution.
The harvests would require a geological POD, since that was due to a major volcanic eruption on Iceland.
You are completely right about gradual reform being the best (that is: 'most stable') way to get things done, since that causes less pushback. My own suggestion above was mainly to show that avoiding a real revolution at the last moment
was possible-- but obviously, the closer you cut it, the more you have to rely on eberything going just right. Any dumb thing can be the spark that lights the fire. The longer back you go and the more gradual your changes, the lower any chance of a real explosion gets.
I think the most stable way to avoid the Revolution altogether is to have some timeline where the more radical Enlightenment thinkers find other things to do with their lives, and where France decides not to get involved in the ARW (can be part of the same POD: the aristocrats who pushed for intervention were inspired by Enlightenment ideals, and a somewhat more subdued and less 'zealous' Enlightenment could easily fail to inspire that in them). Europeans as a whole are less iclined to help out the Americans, and as a result, the ARW is lost in this scernario. That means no example of a previous republican revolution to inspire the French, in addition to there being no radical Enlightenment thinkers suggesting drastic upheavals. That in turn lets the moderate Enlightenment thinkers predominate, and they argue for reforms (including fiscal and economic ones) and a parliamentary monarchy based on the example of Britain. Since 'Enlightenment' isn't seen as intrinsically linked to certain radical thoughts, these ideas find more support among the elite. The failed harvests of the 1780s are a major wake-up call rather than the straw that breaks the camel's back, and in the following years, France sees a series of gradual reforms, at least in part based on the ideas of Voltaire (constitutional monrchy, religious tolerance), Montesquieu (legal reform, constitutionalism), and physiocrats like Turgot and Quesnay (tax reform, free trade, deliberate steos to eliminate the national debt over time). This then accelerates a decade later, when men like Condorcet become the face of the modern, revitalised French state.