Kinda? Lenin’s ideas aren’t a morphing or changing of Marxism, and it certainly wasn’t just the Manifesto, but Marx’s actually important works. Lenin looked at Marxism, studied it, and applied Marxist analysis to his conditions in Tsarist Russia. Notably adding his analysis of Imperialism and Revolution.
Mao did the same thing, applied Marxism (and took inspiration from Lenin) with respect to China’s conditions.
The reason why Marxism-Leninism is by far the most common is because we are still clearly in the age of Imperialism as described by Lenin, and his analysis is still valid. Rejecting Lenin is very unusual for Marxists, because Lenin basically applied Marxism to the contemporary era where Revolution has been delayed due to super-exploitation of the third world in exchange for super-profits.