When making changes to a block of code or block of text, I frequently just comment out the code and rewrite it anew. I might copy-paste existing code (just to avoid stupid transcription errors). If its too large to see both what I'm writing, and the old code, at the same time, I just use two windows on the same file.
This is relevant to writing fiction or non-fiction as well.
For example, I didn't like this, so I commented out:
>though his companions jogged just behind him, he would have barely seen them at all had he look. They ran, with their heads down, attentive only to their feet slapping the muddy earth, tracking the path they followed, their breath ragged.
and wrote this, using the commented-out text as a reference:
The fog was now so dense that he could see nothing ahead of him. He ran with his head down, breath ragged, attentive only to his feet slapping the muddy earth, tracking their path. His companions followed close behind.
This is relevant to writing fiction or non-fiction as well.
For example, I didn't like this, so I commented out:
>though his companions jogged just behind him, he would have barely seen them at all had he look. They ran, with their heads down, attentive only to their feet slapping the muddy earth, tracking the path they followed, their breath ragged.
and wrote this, using the commented-out text as a reference:
The fog was now so dense that he could see nothing ahead of him. He ran with his head down, breath ragged, attentive only to his feet slapping the muddy earth, tracking their path. His companions followed close behind.