In the sentence above, does “in the same sense” mean “to keep the meaning unchanged”?
Yes, it does. They are contrasting various sets of sentences. In the set immediately above the sentence you are asking about, the complement at the end is not required for the meaning, which would be nearly the same with or without that word. To say "The fire is burning" does not communicate as much as "The fire is burning low," for example, but the fire is burning in either case; so "low" is not required for the basic meaning.
The sentence you are asking about is followed by a colon and then another set of sentences. That means that the sentence introduces that set of sentences and applies to them. In those sentences, if you take out the sentence-ending element (the "complement"), the meaning will not be the same at all. Thus, "They are pleading" does not have even remotely the same meaning as "They are pleading guilty."
