Hi Ray

Thank you for the answer, I thought that might be the case. 

As a work around, would it be possible to have a many2many product and BOM field?

Thanks

You would need more than the field, as the logic when the ECO is applied works for a single Product/BoM.

It seems like a low value customization. Duplicating is easy, achieves the same thing, is free, is supported and will not delay an upgrade to a new version.

In our business one ECO can cover many products. Grouping the same change in the different products/BOMs into one ECO would reduce the workload that would be there in repeat and change the ECO number manually.

You can contact Odoo or an Odoo Partner for help customizing Odoo if you cannot live without this feature, it will increase the price of your subscription if we do it, and if most Odoo Partners do it.

Thanks Ray. I shall look into it. Do you think it would be possible in studio or will it have to be coded?

I don't see how this could work in Studio, it would need code.