Why longer range would not break the British blockade

Would long-range diesel warships let Germany escort merchant convoys through the British blockade?

No. Britain would still possess the larger navy and could concentrate against the convoy and its escorts, so diesel endurance would not remove the blockade.

Long range allows warships to raid farther afield, but it does not give Germany command of the sea routes around Britain. A merchant convoy would remain a concentrated target that the larger Royal Navy could find and attack. German escorts would add tactical difficulty without reversing Britain's advantage in ships, bases, and maritime infrastructure. The scenario therefore changes the reach of German surface warfare, not the strategic fact of blockade.