Am I obliged to recertify my product, when a Directive or standard is altered?

No, a product is certified in accordance with the applying Directives and (harmonised) standards at that time. New products that are placed on the market need to placed on the market in accordance with the Directives and standards that apply at that time.

Products, to which important changes have been made with the intention of altering the original operation, the original goal or type, after the product has already been used, for instance by using other components or new deliverers, can be regarded as new products.

Also you, as manufacturer, are responsible for the safe usage of your product. If important alterations have been made to the Directives and (harmonised) standards that apply to your product, then it is advisable to (partially) recertify your product.