What a .dst file actually contains
A sheet set (.dst) is not a drawing, it is an index. It holds the order of sheets, references to the layouts inside your .dwg files, the subset structure and every custom property your title block reads. Because it is an index, editing it separately is safe: the geometry in your drawings is untouched. Sheet Set Editor loads that index, lets you edit everything in a single table and writes the structure back unchanged.
