Not sure if I understand.
IMHO, it belongs to “outliner mode experience”.
I do not now if it will be solved by plugin or by core Obsidian.
There are text editors able to focus on specified portion of dokument, the rest being hidden or locked for editation.
For example https://www.emeditor.com/text-editor-features/more-features/narrowing/
So there is no risk of undesired change for underlying markdown dokument.
Here is even request specifically for this: Ability to freeze parts of a note
keywords: narrow, restrict, focus