I choose the Schleiffen Plan as it was, with one caveat:
I would dedicate all possible efforts towards getting Italy on Germany's side.
This could probably be achieved by using the money that was IOTL used to bribe the Ottomans to join the CP instead to bribe the Austro-Hungarians into ceding South Tyrol to Italy.
The reasoning behind this is simple.
No matter how badly the Italian Army does on the front, she will take up entente resources that could be used in the north.
This is the straw that breaks France's back.
When the race to the channel starts, Germany will have the advantage, and might break through the front.
This will greatly demoralize French troops, and a large enough mutiny could very well result in complete collapse of French lines.
A breakthrough in the north could lead to the BEF abandoning France, so that if France is able to get its act together, it will likely be too late anyway.
Also, Italy will need to be blockaded. This should be relatively easy for the Royal Navy, but maybe not for the French Navy (which was essentially in charge of the Mediterranean), especially when you take into account the Austro-Hungarian Navy and the Ottoman Navy if it does choose to join.
This means the Royal Navy is held up in the Mediterranean battling Italian and Austro-Hungarian fleets, and won't have as big a presence in the North Sea.
This means that the High Seas Fleet may have an upper hand at a Jutland equivalent. A decisive defeat of the Royal Navy will both really demoralize the British people and also break the blockade of Germany.