For starters, you could put a begin and end date on the products in your BoM. (Valid from, valid until)

For good change management, you really need both methods suggested here, and more.

• begin / end dates on BOM components

• revision identifier on products
  

We have deeply nested BOMs, up to 8 levels deep, with thousands of components.

When you revise a component, you need to make a copy of the product with a revision identifier.  Where this revised product is used in an assembly, you set an end date for the previous revision, and a start date for the new revision.

If the revised component is a subassembly, then you also need to make a copy of the BOM for that revised subassembly.  A custom module, doing all of this at once, would be convenient.

I've used the approach proposed by Josse before with reasonable success, although it can be tedious reviewing each part's end-date to determine which parts were included on a product's BoM several revisions back.

Another approach I've used before is to suffix the part number (aka "Internal Reference") with the revision level. For example, part number 2100123-01 for revision 1, 2100123-02 for revision 2, etc.