I don't exactly understand, but I'll try to help. Your first paragraph in particular makes little sense to me.
Do you know that you can save a BOM (or any other) table as an Excel file? That makes it disassociative to changes, but easy to summarize through formulas and/or perpetuate it into other documents.
You can also make an assembly that contains many other assemblies, and then create a BOM of that assembly. Sort it, export, and load total qty info for your purchaser in relation to totality of a project or deliverable or contract or w/e. If you have questions on this, I can try to find and link a recent post of mine where I detail that process a bit more.
I do both of those, and use a BOM template formatted with sorts for export into a hamhanded excel sheet standardized by others.
I use multysheet for 1 file drawing. BOM will be blocks BLOCK01-...BLOCKn. Do not many file for one project.