Footing on an article on censorship in the Soviet Union (the name evades me. It was in Russian and amounted to "what books were burnt"):

No, the Soviet Union did not censor prominent pieces of Communist literature but after a boom in publishing all kinds of left leaning authors in the 1920s the libraries were, for example, forced to surrender a plenty of non-marxist socialists and non-bolshevik marxists (previously such purges concerned, for instance, religious literature). Under Stalin the Soviet Union first defined what pieces have been "prominent pieces" and it were the complete works of Marx, Engels and Lenin (and Stalin, who, however, was dropped during the khrushchev era) which were published in editions spanning dozens of tomes. The different ideological leanings (what was cited in the last few prominent speeches of the general secretary) were mirrored in shortened editions (~4 tomes) and in academics and journalists citing from the same few prominent places.

There were illegal compilations of (partly spurious) quotations published abroad and smuggled into the country in an effort to present the authors in a bad light, but in the USSR the previledge of publishing the classics belonged to very few prominent publishers (such as Politizdat) which have been all pretty good at following the party line.

To slam Stalin, Khrushchev did, for instance, dare to borrow the Marxian notion of the personality cult. It was available in the open in the complete edition before, but of course it didn't get cited or republished separately until the Destalinization.

The Soviet government did indeed suppress certain documents that might be detrimental to the prevailing order. For example, Lenin's famous Testament wasn't first published until 1956, not coincidentally the same year that Khrushchev gave his famous "Secret Speech" denouncing Stalin.

However, texts as far as I'm aware weren't "edited" but rather narrated around in such a way to afford a different interpretation of the original. This can be seen in Stalin's earlier work Foundations of Leninism though these points always bring up debate between different Marxist tendencies.