There are many permutations of products and customers so it is not easy to be exact.
If you make a product which is designed for a specific customer, then yes you should communicate any changes.
If it is a generic off-the-shelf product sold under your own name, it is less clear. It may be that you publish your specifications on your website or catalogue in which case they can be changed and communicated relatively easily. If you do not have this option it is difficult. You may sell through distributors and not know the identity of the customer.
The clause uses the term 'where required' and this does give you a bit of freedom
The line that I would take is that if the change has an impact on how the product is used (eg changes to tensile strength, opacity, friction, legality etc) you should inform the customer where you know who it is.
If it is a food contact material, it may that you need to redo and resend Declarations of Compliance as well.