Hi Marc,

Export your current BoM, with mandatory fields as below
BoM / External ID
BoM Lines / External ID
BoM Lines / Product -> you can use this or use the External ID instead

These 3 are the mandatory, the rest you can add the qty, uom, etc.

After that, you can update the product, qty to consume, uom, etc and reupload your file.

Make sure you test it on development first.

Hope this helps.