Reply To: line by line custom text backfill

I agree with Eugene and Furry. But, if it's not throughout and maybe something like boxed material or sidebars that flow with the text, you could try to make a single-cell table out of those paragraphs with the shading. When text is added or deleted, it will resize.

If you use the character style sheet method for the strikethrough or rule above below, I'd nest through a hard return. Of course, you'd have to have a separate paragraph style sheet for that shaded material.