He did not add to Marx, he only applied Marx to the specific conditions of 20th century Russia. The challenge remains for you to show that Lenin updated Marx or believed that he was.

...This is necessary to pave the way for the solution of the economic problem, i. e., that of the economic transition to socialist principles

Do you understand the context of what you posted? Apparently not. He's alluding to the ongoing international struggles. He knows that socialism will be impossible in Russia without those victories.

Our backwardness has put us in the forefront, and we shall perish unless we are capable of holding out until we receive powerful support from workers who have risen in revolt in other countries."

Source: "Letters on Tactics," 1917

"We are far from having completed even the transitional period from capitalism to socialism. We have never cherished the hope that we could finish it without the aid of the international proletariat. We never had any illusions on that score, and we know how difficult is the road that leads from capitalism to socialism."

Source: "The Tax in Kind," 1921

"We always staked our play upon an international revolution and this was unconditionally right... We counted upon a revolution of the world proletariat and were of the opinion that Europe after the war would rise so rapidly that either the spark of our revolution would kindle it, or that it would kindle our damp squib."

Source: Speech at the 4th Congress of the Comintern

These statements stand in stark contrast to the policy of "Socialism in one Country" of Marxism-Leninism. ML has nothing to do with Marx or Lenin.

It is an insult to the socialist system to say that an “opportunistic and traitorous” Stalin would be able to become a “dictator” within it.

Not even Lenin thought they had reached socialism yet. Even the quote you posted said as much, so I can only assume you can't read.