This is gonna heavily depend upon if the objects/chunks you are having a LLM modify is coherent enough to contain everything it needs within that single chunk. 10kb is gonna be too much to edit as once, hence your post, but you also are going to have issues where you cannot properly piece/chunk out the html file, there will be necessary code ahead and behind the chunks that will be valuable to the entire structure of the page.
even using react and such, your gonna hit walls where there won't be a good enough way to chunk the code out and modify it. this is a context window problem/compute problem, not one that's been solved as of today. HTML would be a bit easier i would venture as far as saying but you would still hit the wall, always in some fashion.