21 C.F.R. § 117.170
(b) You must conduct a reanalysis of the food safety plan as a whole, or the applicable portion of the food safety plan:
(c) You must complete the reanalysis required by paragraphs (a) and (b) of this section and validate, as appropriate to the nature of the preventive control and its role in the facility's food safety system, any additional preventive controls needed to address the hazard identified:
(2) When necessary to demonstrate the control measures can be implemented as designed: