You have one thing right. I know what tankies think it means and I know what it actually means.
What it actually means: The “modernization” of Marxism, the “updating” of the original invariant communist program of the working class from Marx to Lenin.
What tankies, the modernizers, think it means: going against “Marxism-Leninism”, the Soviet State capitalist ideology created by Stalin that has nothing to do with either Marx nor Lenin.
I’m honestly giving people here to much credit by calling them Stalinists. In reality the Stalinists are gone and there’s nothing left of them but goofballs, mostly teenagers, aping their phraseology and aesthetic.