I believe, In any case the proposed building can not be 100% as per design. There will be always variation regarding HVAC equipment selection (e.g. head change wrt actual site installation resulting change in pump selection), Envelope material selection, etc.

Since the credit is design submission, in case if I will ensure % savings are equal to or more than what I have indicated in design submission (no impact on points earned), I do not need to submit the credit again in construction phase.