I am having trouble parsing both of those sentences. Even if I make the change from "It's mean" to "It means", example one is still is not grammatical. "show, showed" and "the realism, the word realism" double up the verb and direct object of the subordinate clause in a non-standard way. The only way I can make sense of this is in oral speech where the speaker changed their phrasing mid-sentence.
The second example is even less clear. I tried to read it as "use" and "uses" and to change "has it owns" to "has its own" and "of narrator" to "of the narrator", but the sentence is still lacking something, probably a direct object for "uses".
To answer your actual question, the meaning is altered because it is not clear what point the author is trying to make and the whole of communication is altered because you end up going over it several times to try to get the intent.
I somehow think (without any particular evidence) that when discussing an abstract topic, it is more important to get the grammar right than when discussing concrete topics because it is harder for the listener or reader to make the leap to what the speaker or author is really trying to convey. If a non-native speaker was talking about, say, a dog rather than the qualities of a genre of literature, you could use general knowledge to fill in some of the gaps and understand the intent better.