Were you saying it wouldn't have mattered to the invasion of Poland or it wouldn't have changed the entire war？
Even if Poland's back was broken in two weeks, if the Germans are sending panzer divisions to the Saar to engage determined French offensives in October then I don't see how Fall Gelb looks anything like it did historically.
It also seems likely Warsaw and even other cities would hold out longer if the Luftwaffe was redeployed.
I also dimly recall something about Germany not having enough ammunition on hand in fall 39 to fight two full campaigns.
No one ever has enough ammunition. There is no such thing as "enough ammunition" in industrialized warfare
And yes my explanation only sought to apply to the situation as of September / October 1939. I didn't mean to say that an early French offensive into the palatinate / Saar wouldn't have any effects, certainly it would change some things. Germany and France get into a big ol shooting match a lot earlier, ammo and supplies get used earlier, some German towns and cities fall. But given that the French even under optimistic assumptions only really get so far before the Germans stop them with numerically superior forces, I don't think it can change the big picture. The French of 1939 didn't have the planes and tanks they had in May 1940, their arms production had only been crash started in the second half of 1938 so the French army and air force of September 1939 was going to have to work prudently with the material it had in the field, and be careful not to not expend it all too fast on high speed, high energy, high casualties operations because the war factories in France were still only starting to produce material in larger numbers whereas the German factories were a bit further on the ramp up to war production.
Ultimately, barring sudden surprises and accidents of history, the German superiority in numbers, and their initially larger war production, will result in a very quick end and reversal to a French advance. You need 3:1 superiority in order to achieve success in frontal attacks, and a push down the Rhine, or across the Rhine, would totally be a frontal attack. The French only have such a superiority in the first 2-3 weeks, are down to parity by mid October, and will face multiple counter offensives with local German superiority by November. So that's when they will fall back onto the maginot line, at the latest.
If they set their mind to a thorough wrecking of the German towns and countryside, demolishing bridges, railways, factories, farms, telephone systems, switches, canals and store houses, they can pretty much forestall any German offensive against the maginot line until at least summer 1940 or so which would (from their point of view) be a very great advantage gained. Hardly a war winning move, though, as they would only be able to to that in the territory seized in those first weeks i.e. the very southwest of Germany, Saar and Palatinate and parts of the Mosel region. The regions facing Belgium and the Netherlands are too far north and not affected. So, there's still going to be a phony war phase, a German buildup, naval battles and 1940 will see the initiative solidly on the German side with greater numbers, better and more weapons, and potentially the same breakthrough successes as historically.
But one thing that is certainly going to make a difference is the fighting spirit and leadership quality of the French army. I mean in some ways these are baked into the scenario, you don't get a strong push into southwest Germany with the mindset and awful leadership of the historical French army of 1939. The offensive mindset, willingness to take losses, and better leadership are prerequisites to them launching such an attack in the first place, let alone pushing it 150 km or so into Germany, against opposition. If they do that they not only have a better army than they had, they would also learn from those weeks of intense operations a lot about their own weaknesses that will make their performance in summer 1940 a lot better. A faster reaction loop at the high command, better coordination, faster rallying of reaction forces, experience with high speed large operations, experience fighting the German armor, that's what was missing in the French army historically in May 1940. Give them that, and they might beat the German offensive altogether, bomb the huge traffic jam in the Ardennes and clog the offensive up before it develops. Doesn't stop the other big push coming through Belgium, doesn't magically make the luftwaffe disappear, but certainly might reduce the risk of catastrophic defeat in May 1940.
Long term, God is on the side of the bigger battalions. Germany with her back secured by uncle Stalin is going to push the French and British badly. But it might stalemate and then the long game sets in, who has more industry and resources and can turn that into combat power. France and UK have the edge there.
