Should quotation marks be used where a quote has been deliberately changed to mean something slightly different?

Quotation marks are used to enclose not only quotations from real sources (i.e. the words that somebody has actually said or written somewhere else), but also ‘quotations’ from imaginary ‘sources’, such as the words ‘spoken’ by an imaginary character, or the words that are given as examples of something that somebody (who needn’t be specified) could say. This last way of using them can be seen throughout this site.

The second sentence that appears in quotation marks in the OP’s example is an instance of that, perfectly correct, use of quotation marks. The OP is, in that example, merely inviting his readers to think about that sentence, while making it clear that no actual source is being quoted. It is immaterial to the correctness of this use of quotation marks that the sentence is formed by modifying the actual quotation that precedes it. Of course when one does something like what OP is doing here, it is very important that the context make it clear which quotations are actual and which are the modifications; in OP’s example that is clear.