No chance for a maginot line...
you miss the war that caused him to think that france NEEDED that kind of defence.
There existed fortresses... they were good enough.
OTL - if the germans had stood on the defence , they would have slaughtered the french easily with 1, maybe 2 armies... another one cover the belgian frontline... and you have an easy Win-scenario for the germans in ww1.
But as was mentioned, the idea was to strike and win a quick war.
if you change this mindset, the germans would do this:
a.) build up strategic reserves, so they could stay in a war for longer
b.) look for allies outside the german bight...
c.) look for methods to supply your home front with strategic materials (either by neutrals or by trading subs)
d.) make sure that at last some neutrals will not get violated (as the dutch... if the USA keep them supplied, germany is untouchable - that was the idea of OTL, but if you face a long war, you prepare much better for that)
e.) have a plan
OTL was "quick invasion of france, then fight to break the will of russia"...
f.) use your navy usefully...
OTL the germans expected from 1911 that UK was an enemy. in a short war this is no problem, because beating france mean it is over before the british could do some bad things to your economy.
If you expect a long war, you need better preparation (infact you need that too in a short war.. but we do not want to wank them).
Russia - was seen as the true deadly enemy... in a long war you coordinate better with your only allied partner - AH. So you propably avoid the mess of Conrads mobilisation plans... that alone could win you the war, but again, that is basically a wank in itself.
So, you have a plan, a strategy.
You get modern stuff (the Haber-Bosch-facilities that are needed to produce nitrates - if you do not struggle in a war in 1914, but say in 1916 germany could FULLY supply its harvest AND produce much more ammunition... bad news for its enemies).
If your strategy mean you stay on defence in the west, you want to strike in the east. Right?
So dig in, slaughter the "frogs" and "ketchups" if they attack, have some eyes on the dutch (british invasion) and belgium (british invasion, french invasion),... otherwise march east...
you have no other chance in that scenario.
So - the fleet will support your big invasion stuff on the moon island - in 1914, press the russian fleet in a corner quickly... , then try to support your advancing armies by some invasions at the coast. German imperial fleet of 1916 (the year we start this conflict?) is able to do that.
the armies: you have enlarged your armies by 1 or 2, after all you calculate with a long bloody war (or you would not build your defence system in the west)... so you could defend in the west with 4 armies and still send 5 to the east, maybe 6.
We know that this mean the russians are doomed... they get slaughtered from day 1 of this war, that will never change.
If that happens, and in the same time the french (and maybe - no invasion in belgium, so unclear if uk enters early in that war) die in huge numbers achiving nothing at the border, italy will not enter this war. Not at all... so austria is in better shape, serbia dies in 1915, bulgaria enters the conflict earlier (possible)
The osmans got their 2 battleships, have recovered from the balkan-wars... so russia need more forces against them.
If UK is neutral till that point they have to think about the consequences of that war. Better to negotiate a peace (and hope to get influence)...
if they are dump they are in the war. So expect also the british dying useless in the trenches.
If UK and France attack belgium -> no rape of belgium but belgium a german ally... USA will not tolerate violating of their neutral rights... expect large US convoys moving through the war zone to the dutch... and they will sell to germany because the evil british and french threatens them.
Russia in the meantime get slaughtered...
Game over in 1918 latest.
So, sometimes in 1918 the germans will turn to the west and now expect some huge defeats for the thinned french and british forces, against the might of germany, belgium, austria-Hungaria... with no pro-british leaning neutrals...